Data transmission system, data transmission apparatus, data reception apparatus, and data transmission method

ABSTRACT

Provided are a data transmission system as well as data transmission method, data transmission apparatus and data reception apparatus which can maintain synchronization between transmission and reception even when the transmission apparatus, the reception apparatus and the transmission path do not operate on the same clock.  
     A data packet which is obtained by omitting a preamble or a parity or both of them from the data generated by the data generation means ( 111 ) and adding a data length field and spare bits is set as an access unit and is transmitted from the transmission apparatus ( 110 ) to the transmission path ( 100 ), and the reception apparatus ( 120 ) adds, to the received data, the preamble or the parity or both of them which have been omitted to reconstruct data, and adjusts the rate of data reading clock for transmitting data from the reception-side buffer means ( 124 ) to the data processing means ( 121 ) on the basis of the buffer accumulated amount in the clock control means ( 126 ).

TECHNICAL FIELD

[0001] The present invention relates to a data transmission system inwhich a transmission path is shared by a plurality of communicationapparatuses and which perform data transmission using synchronouschannels, as well as data transmission method, data transmissionapparatus, and data reception apparatus, and particularly relates to thesystem, method and apparatuses which achieve synchronization ofoperations between the transmission apparatus and reception apparatusconnected to each other via the transmission path.

BACKGROUND ART

[0002] In recent years, the study of the communication method fortransmitting, via a common bus, digital data such as digitized video,audio data, computer data and the like is eagerly made. A conventionaltransmission system, for example, the communication system disclosed inJapanese Published Patent Application No. Hei.9-107373, will bedescribed as an example, with using FIG. 14. In FIG. 14, referencenumeral 100 denotes a transmission path, and numeral 101 denotes a clockcontrol means for controlling a clock of the transmission path 100.Further, reference numeral 1410 denotes a transmission apparatuscomprising a data generation means 1411 and a first communicationcontrol means 112, and reference numeral 1420 denotes a receptionapparatus comprising a data processing means 1421 and a secondcommunication control means 122.

[0003] Hereinafter, the operation will be described.

[0004] The transmission system shown in FIG. 14 transmits data from thetransmission apparatus 1410 to the reception apparatus 1420 via thetransmission path 100. The transmission path 100 operates on the basisof a clock which is controlled by the clock control means 101, and thefirst communication control means 112 in the transmission apparatus 1410and the second communication control means 122 in the receptionapparatus 1420, which are connected to the transmission path 100,extract the clock when receiving data from the transmission path 100,and utilizes the clock for data processing inside.

[0005] The transmission apparatus 1410 inputs the extracted clock to thedata generation means 1411. The data generation means 1411 generatestransmission data using the input clock and transmits the transmissiondata to the first communication control means 112. The firstcommunication control means 112 outputs the transmission data to thetransmission path 100.

[0006] In the reception apparatus 1420, the second communication controlmeans 122 receives the transmission data and transmits the same to thedata processing means 1421. Further, the second communication controlmeans 122 simultaneously extracts the clock and transmits the clock tothe data processing means 1421. The data processing means 1421 uses theextracted clock to process the transmission data.

[0007] In the procedure described above, the data generation in the datageneration means 1411 and the data processing in the data processingmeans 1421 are performed by using the same clock, and therebysynchronization between the transmission apparatus 1410 and thereception apparatus 1420 can be achieved and the transmission systemperforms operation without failure.

[0008] The network as described above is used for the vehicle-mountedmultimedia network MOST (Media Oriented Systems Transport) using opticalfiber for transmission, and the like, and the network and an apparatusconnected thereto operate by synchronizing clocks thereof, therebyreducing buffers and the like to be incorporated into the apparatus toattempt reduction in costs or facilitation of connection of variousapparatuses to the network.

[0009] Moreover, as for the network (IEEE1394) transmission of IEC60958format, for example, a demodulation apparatus and a signal processorwhich receive the IEC60958 format data and demodulate the data in atransmission apparatus is disclosed in Japanese Published PatentApplication No. 2000-149461.

[0010] As described above, in the conventional data transmission system,and data transmission method, the transmission apparatus 1410, receptionapparatus 1420, and transmission path 100 operates on the same clock toperform data generation and processing, thereby maintainingsynchronization between transmission and reception.

[0011] However, in the conventional construction described above, in acase where the data generation means 1411 on the side of thetransmission apparatus 1410 has a specific clock and transmits thetransmission data on the basis of the specific clock, or in a systemwhere while a clock source of the data generation means 1411 and a clocksource of the transmission path 100 are the same, the transmissionapparatus 1410 and the transmission path 100 operate respectively on theclocks of different rates in specifications, there is a problem that thesynchronization in data processing cannot be achieved.

[0012] Further, in a system where while the data generation means 1411and the transmission path 100 operate on the clock of the same rate inspecifications, a synchronization is exactly caused due to clock sourcesthereof being different from each other, there is a problem that anoverflow or underflow of the transmission data occurs in thetransmission apparatus 1410 during the operation of the datatransmission system.

[0013] The present invention is made to solve the above-describedproblems, and an object of the present invention is to provide a datatransmission system, data transmission apparatus, data receptionapparatus, and data transmission method which can maintainsynchronization between transmission and reception even when thetransmission apparatus, reception apparatus, and transmission path donot operate on the same clock.

DISCLOSURE OF THE INVENTION

[0014] The data transmission system according to Claim 1 of the presentinvention is a data transmission system in which one or moretransmission apparatus and one or more reception apparatus are connectedto each other via a transmission path and data are transmitted from thetransmission apparatus to the reception apparatus with using an accessunit which emerges at certain time intervals and is allocated for thetransmission path, wherein the transmission apparatus comprises a datapacket generation means for receiving transmission data which iscomposed of consecutive data frames and has a format which includes apreamble indicating a start of the data frame, or a parity for detectingan error in the data frame, or both of them, and omitting the preamble,or the parity, or both of them, from one or more data frames included inthe transmission data received within the certain time intervals, addingto this resultant a data length field indicating the number of bits ofsignificant data, and setting the remaining spare portion as spare bits,thereby generating a data packet composing the access unit over itsentire length, and the reception apparatus comprises a data extractionmeans for receiving the access unit, and adding the preamble, or theparity, or both of them, which have been omitted by the data packetgeneration means, thereby reconstructing the data frame.

[0015] Therefore, even when there is a difference between a clock rateof the transmission path and a clock used for the processing inside thetransmission apparatus, the clock difference can be absorbed byadjusting the spare bit length, thereby realizing synchronization inoperations between the transmission apparatus and the receptionapparatus.

[0016] Further, according to the data transmission system of Claim 2 ofthe present invention, in the data transmission system as defined inClaim 1, the reception apparatus comprises: a buffer means fortemporarily accumulating the data frames reconstructed by the dataextraction means, and a buffer control means for monitoring theaccumulated data amount in the buffer means and adjusting a data readingrate from the buffer means in accordance with the increase or decreasein the accumulated data amount.

[0017] Therefore, the reception apparatus can perform data processing atthe same clock rate as that of the transmission apparatus, therebyrealizing the synchronization of the system.

[0018] Further, according to the data transmission system of Claim 3 ofthe present invention, in the data transmission system as defined inClaim 1, the transmission apparatus comprises a time-informationgeneration means for generating a time based on a clock of thetransmission data, and the data packet generation means also adds thetime-information as well as the data length field and sets the remainingspare portion as spare bits, thereby composing the access unit over theentire length, and the reception apparatus comprises: a buffer means fortemporarily accumulating the data frames reconstructed by the dataextraction means, a clock control means for reproducing the timegenerated by the transmission apparatus by using the time-informationwhich the data extraction means read from within the access unitconstructed by the data packet generation means, and a buffer controlmeans for adjusting a data reading rate from the buffer means based on aclock which is synchronized with a time reproduced by the clock controlmeans.

[0019] Therefore, even when there is a difference between a clock of thetransmission data and a clock of the transmission path, the receptionapparatus reads the time-information created from the clock on the sideof the transmission apparatus and adjusts the data reading rate, therebyrealizing synchronization of the system.

[0020] Further, according to the data transmission system of Claim 4 ofthe present invention, in the data transmission system as defined inClaim 1 or Claim 2, the data packet generation means also adds apreamble location pointer indicating a location of the first preamble inthe data frame, and a type of the preamble of the data frame, thepreamble being indicated by the preamble location pointer, as well asthe data length field, and setting the remaining spare portion as sparebits, thereby constructing the access unit over the entire length.

[0021] Therefore, even when the transmission data gets disconnectedhalfway during transmitting transmission data from the transmissionapparatus via the transmission path, reconstruction of a frame on theside of the reception apparatus can be easily realized with usinginformation indicating the location pointer and the type of thepreamble, which is added to the transmission data.

[0022] Further, according to the data transmission system of Claim 5 ofthe present invention, in the data transmission system as defined in anyof Claims 1 to 4, the transmission data format includes a specific fieldhaving a value specific to an application, the data packet generationmeans also omits the specific field as well as the preamble, or theparity, or both of them, and the data extraction means also adds thespecific field as well as the preamble, or the parity, or both of them,thereby reconstructing the data frame.

[0023] Therefore, by omitting unnecessary data for data transmission,data which can be transmitted for each packet via the transmission pathcan be effectively utilized, and the reception apparatus adds theomitted data to reconstruct the data frame, thereby demodulating thetransmission data properly.

[0024] Further, according to the data transmission system of Claim 6 ofthe present invention, in the data transmission system as defined in anyof Claims 1 to 5, the data length field indicates the number of bits ofspare bits.

[0025] Thereby, when packetizing the transmission data, it is possibleto secure a field into which an application can be arbitrarily written.

[0026] Further, the data transmission system according to Claim 7 of thepresent invention is a data transmission system in which one or moretransmission apparatus and one or more reception apparatus are connectedto each other via a transmission path and data are transmitted from thetransmission apparatus to the reception apparatus with using an accessunit which emerges at certain time intervals and is allocated for thetransmission path, wherein the transmission apparatus comprises a datapacket generation means for receiving transmission data which iscomposed of consecutive data frames and has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for the transmissionpath, grouping into a processing unit a plurality of the data frames ofthe received transmission data and corresponding to a period equal to anintegral multiple of the time intervals at which the access unitemerges, dividing the processing unit into transmission path frames eachof which is the data amount which can be accommodated in the accessunit, thereby generating a data packet composing the access unitincluding the transmission path frame, and the reception apparatuscomprises a data extraction means for receiving the access unit,reconstructing the processing unit from one or more of the receivedaccess units, and further reconstructing the consecutive data frames.

[0027] Therefore, in a case where transmission data are transmittedwithout being omitted because of, for example, the preamble and the likebeing unable to be omitted from the transmission data, even when thereis a difference between a clock rate of the transmission path and aclock rate used for the processing inside the transmission apparatus, itis possible to absorb the clock difference by grouping a plurality ofdata frames into a processing unit, dividing the same into thetransmission path frames respectively, and transmitting the same dividedfor each access unit including the transmission path frame. Further, itis possible to reconstruct the data frames from the access units on theside of the reception apparatus, thereby realizing the synchronizationof the system.

[0028] Further, according to the data transmission system of Claim 8 ofthe present invention, in the data transmission system as defined inClaim 7, the data packet generation means enters one or more bits ofsynchronization data indicating a start of the processing unit into oneor more access units, and the data extraction means detects the startinglocation of the processing unit by receiving the synchronization data.

[0029] Therefore, a data start location of the transmitted data can beeasily detected.

[0030] Further, according to the transmission system of Claim 9 of thepresent invention, in the data transmission system as defined in Claim8, the data packet generation means enters one or more bits ofdiscrimination data which are different from a value of thesynchronization data, which discrimination data indicate that thesynchronization data are not included in the access unit, into positionin the access unit in which the synchronization data are not entered.

[0031] Therefore, error detection of the frame including synchronizationdata can be eliminated, performing more reliable transmission.

[0032] Further, the data transmission system according to Claim 10 ofthe present invention is a data transmission system in which one or moretransmission apparatus and one or more reception apparatus are connectedto each other via a transmission path and data are transmitted from thetransmission apparatus to the reception apparatus with using an accessunit which emerges at certain time intervals and is allocated for thetransmission path, wherein the transmission apparatus comprises a datapacket generation means for receiving transmission data which iscomposed of consecutive data frames, has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for the transmissionpath, and has a format including a preamble indicating a start of thedata frame, or a parity for detecting an error in the data frame, orboth of them, omitting the preambles, or the parities, or both of them,from a plurality of the data frames of the received transmission dataand corresponding to a period equal to an integral multiple of the timeintervals at which the access unit emerges to set the resultant as oneprocessing unit, dividing the processing unit into transmission pathframes each of which is the data amount which can be accommodated in theaccess unit, thereby generating a data packet composing the access unitincluding the transmission path frame, and the reception apparatuscomprises a data extraction means for receiving the access unit,reconstructing the processing unit from one or more of the receivedaccess units, and further adding the preambles, or the parities, or bothof them, which have been omitted by the data packet generation means,thereby reconstructing the data frames.

[0033] Therefore, even when there is a difference between a clock rateof the transmission path and a clock rate used for the processing insidethe transmission apparatus, unnecessary data for transmittingtransmission data are omitted and packetization into transmission datapacket is performed, and thereafter the transmission is made for each ofthe access units and thereby the clock difference can be absorbed.Further the reception apparatus extracts the transmission data packetfrom an access unit of data received, and adds, to the transmission datapacket, the data which have been omitted at the transmission, therebyreconstructing the data frame and realizing the synchronization betweenthe apparatuses in the system.

[0034] Further, according to the data transmission system of Claim 11 ofthe present invention, in the data transmission system as defined inClaim 10, the data packet generation means enters one or more bits ofsynchronization data indicating a start of the processing unit into oneor more access units, and the data extraction means detects the startinglocation of the processing unit by receiving the synchronization data.

[0035] Therefore, a data start location of the transmitted data can beeasily detected.

[0036] Further, according to the data transmission system of Claim 12 ofthe present invention, in the data transmission system as defined inClaim 11, the data packet generation means enters one or more bits ofdiscrimination data which are different from a value of thesynchronization data, which discrimination data indicate that thesynchronization data are not included in the access unit, into positionin the access unit in which the synchronization data are not entered.

[0037] Therefore, error detection of the frame including synchronizationdata can be eliminated, performing more reliable transmission.

[0038] Further, according to the data transmission system of Claim 13 ofthe present invention, in the data transmission system as defined in anyof Claims 10 to 12, the transmission data format includes a specificfield having a value specific to an application, and the data packetgeneration means also omits the specific field as well as the preamble,or the parity, or both of them, and the data extraction means also addsthe specific field as well as the preamble, or the parity, or both ofthem, thereby reconstructing the data frame.

[0039] Therefore, by omitting unnecessary data for data transmission,data which can be transmitted for each packet via the transmission pathcan be effectively utilized, and further the reception apparatus addsthe omitted data to reconstruct data frames, thereby demodulatingtransmission data properly.

[0040] Further, according to the data transmission system of Claim 14 ofthe present invention, in the data transmission system as defined in anyof Claims 1 to 6, and Claims 10 to 13, the transmission data format is aformat defined by IEC60958.

[0041] Therefore, the transmission data in format defined by IEC60958can be transmitted from the transmission apparatus to the receptionapparatus via the transmission path with maintaining thesynchronization.

[0042] Further, according to the data transmission system of Claim 15 ofthe present invention, in the data transmission system as defined in anyof Claims 1 to 14, the transmission path is a serial bus.

[0043] Therefore, data can be more quickly transmitted via thetransmission path.

[0044] Further, the data transmission apparatus according to Claim 16 ofthe present invention is a data transmission apparatus connected to atransmission path, which transmits data with using an access unitallocated for the transmission path, and the data transmission apparatuscomprises a data packet generation means for receiving transmission datawhich is composed of consecutive data frames and has a format whichincludes a preamble indicating a start of the data frame, or a parityfor detecting an error in the data frame, or both of them, omitting thepreamble or the parity, or both of them, from one or more data framesincluded in the transmission data transmitted with using the accessunit, adding to this resultant a data length field indicating the numberof bits of significant data, and setting the remaining spare portion asspare bits, thereby generating a data packet composing the access unitover its entire length.

[0045] Therefore, a preamble or a parity, or both of them, which are notinvolved in the data processing, are omitted, and instead thereof, afield indicating the number of significant data bits required for datareproduction and spare bits for adjusting the transmission rate areadded to the data to be transmitted.

[0046] Further, according to the data transmission apparatus of Claim 17of the present invention, the data transmission apparatus as defined inClaim 16 comprises a time-information generation means for generating atime based on a clock of the transmission data, and in the datatransmission apparatus the data packet generation means also adds thetime-information as well as the data length field, and sets theremaining spare portion as spare bits, thereby generating a data packetcomposing an access unit over its entire length.

[0047] Therefore, even when there is a difference between a clock of thetransmission data and a clock of the transmission path, time-informationcreated from the clock on the side of the transmission apparatus istransmitted, thereby realizing the synchronization of the system on thebasis of the time-information.

[0048] Further, according to the data transmission apparatus of Claim 18of the present invention, in the data transmission apparatus as definedin Claim 16, the data packet generation means also adds a preamblelocation pointer indicating a location of the first preamble in the dataframe, and a type of the preamble of the data frame, the preamble beingindicated by the preamble location pointer, as well as the data lengthfield, and sets the remaining spare portion as spare bits, therebygenerating a data packet composing the access unit over its entirelength.

[0049] Therefore, when the transmission data are transmitted via thetransmission path from the transmission apparatus, even if thetransmission data gets disconnected halfway, the reception apparatus caneasily realize reconstruction of a frame by using information indicatingthe location pointer and the type of the preamble, which is added to thetransmission data transmitted from the transmission apparatus.

[0050] Further, according to the data transmission apparatus of Claim 19of the present invention, in the data transmission apparatus as definedin any of Claims 16 to 18, the transmission data format includes aspecific field having a value specific to an application, and the datapacket generation means also omits the specific field as well as thepreamble, or the parity, or both of them.

[0051] Therefore, by omitting unnecessary data for data transmission,data which can be transmitted for each packet via the transmission pathcan be effectively utilized.

[0052] Further, according to the data transmission apparatus of Claim 20of the present invention, in the data transmission apparatus as definedin any of Claims 16 to 19, the data length field indicates the number ofbits of spare bits.

[0053] Thereby, when packetizing the transmission data, it is possibleto secure a field into which an application can be arbitrarily written.

[0054] Further, the data transmission apparatus according to Claim 21 ofthe present invention is a data transmission apparatus connected to atransmission path, which transmits data with using an access unit whichemerges at certain time intervals and is allocated for the transmissionpath, and the data transmission apparatus comprises a data packetgeneration means for receiving transmission data which is composed ofconsecutive data frames and has a data transfer rate, a relationship ofan integer ratio being established between the data transfer rate and adata transfer rate allocated for the transmission path, grouping into aprocessing unit a plurality of the data frames of the receivedtransmission data and corresponding to a period equal to an integralmultiple of the time intervals at which the access unit emerges,dividing the processing unit into transmission path frames each of whichis the data amount which can be accommodated in the access unit, therebygenerating a data packet composing the access unit including thetransmission path frame.

[0055] Therefore, even when the transmission data are transmittedwithout being omitted because of, for example, the preamble and the likebeing unable to be omitted from the transmission data, the difference inclock between the transmission apparatus and the transmission path isabsorbed, thereby realizing synchronization.

[0056] Further, according to the data transmission apparatus of Claim 22of the present invention, in the data transmission apparatus as definedin Claim 21, the data packet generation means enters one or more bits ofsynchronization data indicating a start of the processing unit into oneor more access units.

[0057] Therefore, transmission data having a data start location whichcan be easily detected can be obtained.

[0058] Further, according to the data transmission apparatus of Claim 23of the present invention, in the data transmission apparatus as definedin Claim 22, the data packet generation means enters one or more bits ofdiscrimination data which are different from a value of thesynchronization data, which discrimination data indicate that thesynchronization data are not included in the access unit, into positionin the access unit in which the synchronization data are not entered.

[0059] Therefore, more reliable transmission data whose frame includingsynchronization data can be prevented from being erroneously detectedcan be obtained.

[0060] Further, the data transmission apparatus according to Claim 24 ofthe present invention is a data transmission apparatus connected to atransmission path, which transmits data with using an access unit whichemerges at certain time intervals and is allocated for the transmissionpath, and the data transmission apparatus comprises a data packetgeneration means for receiving transmission data which is composed ofconsecutive data frames, has a data transfer rate, a relationship of aninteger ratio being established between the data transfer rate and adata transfer rate allocated for the transmission path, and has a formatincluding a preamble indicating a start of the data frame, or a parityfor detecting an error in the data frame, or both of them, omitting thepreambles, or the parities, or both of them, from a plurality of thedata frames of the received transmission data and corresponding to aperiod equal to an integral multiple of the time intervals at which theaccess unit emerges to set the resultant as one processing unit,dividing the processing unit into transmission path frames each of whichis the data amount which can be accommodated in the access unit, therebygenerating a data packet composing the access unit including thetransmission path frame.

[0061] Therefore, even when there is a difference between a clock rateof the transmission path and a clock used for the processing inside thetransmission apparatus, unnecessary data for transmitting transmissiondata are omitted to be packetized, and then the transmission is made forevery number of bits of the access unit allocated for the transmissionpath, thereby absorbing the clock difference.

[0062] Further, according to the data transmission apparatus of Claim 25of the present invention, in the data transmission apparatus as definedin Claim 24, the data packet generation means enters one or more bits ofsynchronization data indicating a start of the processing unit into oneor more access units.

[0063] Therefore, the transmission data having a data start locationwhich can be easily detected can be obtained.

[0064] Further, according to the data transmission apparatus of Claim 26of the present invention, in the data transmission apparatus as definedin Claim 25, the data packet generation means enters one or more bits ofdiscrimination data which are different from a value of thesynchronization data, which discrimination data indicate that thesynchronization data are not included in the access unit, into positionin the access unit in which the synchronization data are not entered.

[0065] Therefore, more reliable transmission data whose frame includingsynchronization data can be prevented from being erroneously detectedcan be obtained.

[0066] Further, according to the data transmission apparatus of Claim 27of the present invention, in the data transmission apparatus as definedin any of Claims 24 to 26, the transmission data format includes aspecific field having a value specific to an application, and the datapacket generation means also omits the specific field as well as thepreamble, or the parity, or both of them.

[0067] Therefore, by omitting unnecessary data for data transmission,data which can be transmitted for each packet via the transmission pathcan be effectively utilized.

[0068] Further, according to the data transmission apparatus of Claim 28of the present invention, in the data transmission apparatus as definedin any of Claims 16 to 20 and Claims 24 to 27, the transmission dataformat is a format defined by IEC60958.

[0069] Therefore, the transmission data in the format defined byIEC60958 can be transmitted via the transmission path to the side ofreception apparatus with maintaining synchronization.

[0070] Further, according to the data transmission apparatus of Claim 29of the present invention, in the data transmission apparatus as definedin any of Claims 16 to 28, the transmission path is a serial bus.

[0071] Therefore, data can be more quickly transmitted via thetransmission path.

[0072] Further, the data reception apparatus according to Claim 30 ofthe present invention is a data reception apparatus which is connectedto a transmission path and receives a data packet obtained by omittingthe preamble, or the parity, or both of them, from one or more dataframes included in the transmission data which are transmitted withusing an access unit which emerges at certain time intervals and isallocated for the transmission path, adding to this resultant a datalength field indicating the number of bits of significant data, settingthe remaining spare portion as spare bits and composing the access unitover its entire length, and the data reception apparatus comprises adata extraction means for receiving the access unit and adding theretothe preamble of the transmission data, or the parity thereof, or both ofthem, which have been omitted, thereby reconstructing the data frame.

[0073] Therefore, data having a format in which a preamble or a parity,or both of them, of the transmission data, which have been omitted atthe transmission are restored, can be reproduced.

[0074] Further, according to the data reception apparatus of Claim 31 ofthe present invention, the data reception apparatus as defined in Claim30 comprises: a buffer means for temporarily accumulating thereconstructed data frames, and a buffer control means for monitoring theaccumulated data amount in the buffer means and adjusting a data readingrate from the buffer means in accordance with the increase or decreasein the accumulated data amount.

[0075] Therefore, by adjusting data reading rate, the data processingcan be performed at the same clock rate as that of the transmissionapparatus, thereby realizing synchronization of the system.

[0076] Further, according to the data reception apparatus of Claim 32 ofthe present invention, the data reception apparatus as defined in Claim30 comprises: a buffer means for temporarily accumulating thereconstructed data frames, a clock control means for reproducing a timewith using time-information which the data extraction means read fromwithin the constructed access unit, and a buffer control means foradjusting a data reading rate from the buffer means based on a clockwhich is synchronized with a time reproduced by the clock control means.

[0077] Therefore, even when there is a difference between a clock of thetransmission data and a clock of the transmission path, thetime-information created from the clock on the side of the transmissionapparatus is received and read, and the data reading rate is adjusted onthe basis of the time-information, thereby realizing synchronization ofthe system.

[0078] Further, the data reception apparatus according to Claim 33 ofthe present invention is a data reception apparatus which is connectedto a transmission path and which receives a data packet obtained byomitting preambles each indicating a start of a data frame, or paritiesfor detecting errors in the data frames, or both of them, from aplurality of data frames corresponding to a period equal to an integralmultiple of time intervals at which the access unit emerges, which dataframes are transmitted with using the access unit which emerges atcertain time intervals and is allocated for the transmission path, toset the resultant as one processing unit, and dividing the processingunit into transmission path frames each of which is the data amountwhich can be accommodated in the access unit, and composing the accessunit including the transmission path frame, and the data receptionapparatus comprises a data extraction means for receiving the accessunit, reconstructing the processing unit from one or more of thereceived access units, adding to the processing unit the omittedpreamble or parity, or both of them, thereby reconstructing the dataframe.

[0079] Therefore, the received data are separated into transmission datapackets and the data which have been omitted at the transmission areadded to the transmission data packet, reproducing data having a formatin which a preamble or a parity, or both of them, of the transmissiondata, which have been omitted at the transmission, are restored.

[0080] Further, according to the data reception apparatus of Claim 34 ofthe present invention, in the data reception apparatus as defined inClaim 33, the data extraction means detects the starting location of theprocessing unit by receiving one or more access units including one ormore bits of synchronization data indicating the start of the processingunit.

[0081] Therefore, a data start location of the transmitted data can beeasily detected.

[0082] Further, according to the data reception apparatus of Claim 35 ofthe present invention, in the data reception apparatus as defined in anyof Claims 30 to 34, the transmission data format includes a specificfield having a value specific to an application, and the data extractionmeans adds the specific field as well as the preamble, or the parity, orboth of them, according to a data frame of the transmission data,thereby reconstructing the data frame.

[0083] Therefore, the transmission data can be properly demodulated,thereby realizing synchronization of the system.

[0084] Further, according to the data reception apparatus of Claim 36 ofthe present invention, in the data reception apparatus as defined in anyof Claims 30 to 35, the transmission data format is a format defined byIEC60958.

[0085] Therefore, transmission data in the format defined by IEC60958can be received via the transmission path with maintainingsynchronization with the transmission apparatus.

[0086] Further, according to the data reception apparatus of Claim 37 ofthe present invention, in the data reception apparatus as defined in anyof Claims 30 to 36, the transmission path is a serial bus.

[0087] Therefore, the transmission data can be more quickly received viathe transmission path.

[0088] Further, the data transmission method according to Claim 38 ofthe present invention comprises a data packet generation step ofomitting a preamble indicating a start of a data frame, or a parity fordetecting an error in the data frame, or both of them, from one or moredata frames included in the transmission data which is composed ofconsecutive data frames and has a format which includes the preamble, orthe parity, or both of them, adding to this resultant a data lengthfield indicating the number of bits of significant data of the frame,and setting the remaining spare portion as spare bits, and composing anaccess unit allocated for the transmission path over the entire length,thereby transmitting the access unit to the transmission path, and adata extraction step of receiving the access unit and adding to theaccess unit the preamble or the parity, or both of them, which have beenomitted in the data packet generation step, thereby reconstructing thedata frame.

[0089] Therefore, even when there is a difference between a clock rateof the transmission path and a clock used for the processing inside thetransmission apparatus, the clock difference can be absorbed byadjusting the spare bit length, and further the reception apparatus addsthe data which have been omitted at the transmission, and can performthe data processing at the same clock rate as that of the transmissionapparatus by adjusting the data reading rate, thereby realizingsynchronization of the system.

[0090] Further, according to the data transmission method of Claim 39 ofthe present invention, in the data transmission method as defined inClaim 38, the transmission data format includes a specific field havinga value specific to an application, and the data packet generation stepomits the specific field as well as the preamble, or the parity, or bothof them, and the data extraction step also adds the specific field aswell as the preamble, or the parity, or both of them, therebyreconstructing a frame.

[0091] Therefore, by omitting unnecessary data for data transmission,data which can be transmitted for each packet via the transmission pathcan be effectively utilized. Further, the reception apparatus adds theomitted data to reconstruct data frame and thereby transmission data canbe demodulated properly, and therefore synchronization of the system canbe realized.

[0092] Further, the data transmission method according to Claim 40 ofthe present invention comprises: a data packet generation step ofreceiving transmission data which has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for a transmissionpath, and which transmission data is composed of consecutive dataframes, grouping into a processing unit a plurality of the data framesof the received transmission data and corresponding to a period equal toan integral multiple of time intervals at which the access unit emerges,dividing the processing unit into transmission path frames each of whichis the data amount which can be accommodated in the access unit, therebygenerating a data packet composing the access unit including thetransmission path frame, and a data extraction step of receiving theaccess unit, reconstructing the processing unit from one or more of thereceived access units, and further reconstructing the consecutive dataframes.

[0093] Therefore, in a case where transmission data are transmittedwithout being omitted because of, for example, the preamble and the likebeing unable to be omitted from the transmission data, even when thereis a difference between a clock rate of the transmission path and aclock rate used for the processing inside the transmission apparatus, itis possible to absorb the clock difference by grouping a plurality ofdata frames into a processing unit, dividing the same into thetransmission path frames respectively, and transmitting the same dividedfor each access unit including the transmission path frame. Further, itis possible to reconstruct the data frame from the processing units onthe side of the reception apparatus, thereby realizing synchronizationbetween the apparatuses in the system.

[0094] Further, the data transmission method according to Claim 41 ofthe present invention comprises: a data packet generation step ofreceiving transmission data which has a data transfer rate, arelationship of an integer ratio being established between the datatransfer rate and a data transfer rate allocated for a transmissionpath, and which transmission data is composed of consecutive data framesand has a format including a preamble indicating a start of the dataframe, or a parity for detecting an error in the data frame, or both ofthem, omitting the preamble, or the parity, or both of them, from aplurality of the data frames of the received transmission data andcorresponding to a period equal to an integral multiple of timeintervals at which the access unit emerges to set the resultant as oneprocessing unit, dividing the processing unit into transmission pathframes each of which is the data amount which can be accommodated in theaccess unit, thereby generating a data packet composing the access unitincluding the transmission path frame, and a data extraction step ofreceiving the access unit, reconstructing the processing unit from oneor more of the received access units, adding to the processing unit thepreamble, or the parity, or both of them, which have been omitted in thedata packet generation step, thereby reconstructing the data frame.

[0095] Therefore, even when there is a difference between a clock rateof the transmission path and a clock used for the processing inside thetransmission apparatus, unnecessary data for transmitting thetransmission data are omitted and packetization is performed andthereafter transmission is made for every number of bits of the accessunit allocated for the transmission path, thereby absorbing the clockdifference. Further, the reception apparatus reconstructs the data framefrom the processing unit, thereby realizing synchronization betweenapparatuses in the system.

[0096] Further, according to the data transmission method of Claim 42 ofthe present invention, in the data transmission method as defined inClaim 41, the transmission data format includes a specific field havinga value specific to an application, and the data packet generation stepomits the specific field as well as the preamble, or the parity, or bothof them, and the data extraction step also adds the specific field aswell as the preamble, or the parity, or both of them, therebyreconstructing a frame.

BRIEF DESCRIPTION OF THE DRAWINGS

[0097]FIG. 1 is a block diagram illustrating a configuration of a datatransmission system according to embodiments of the present invention.

[0098]FIG. 2 is a diagram illustrating an IEC60958 format.

[0099]FIG. 3 is a diagram illustrating an example of bi-phasemodulation.

[0100]FIG. 4 is a diagram illustrating a preamble in IEC60958.

[0101]FIG. 5 is a diagram illustrating a transmission path format inMOST.

[0102]FIG. 6 is a diagram illustrating a process flow chart of a datatransmission apparatus according to the embodiments of the presentinvention.

[0103]FIG. 7 is a diagram illustrating a packetized format oftransmission data used in the data transmission system according to afirst embodiment of the present invention.

[0104]FIG. 8 is a diagram illustrating a process flow chart of a datareception apparatus according to the embodiments of the presentinvention.

[0105]FIG. 9 is a diagram illustrating a clock control method accordingto the embodiments of the present invention.

[0106]FIG. 10 is a diagram illustrating a packet construction used in adata transmission system according to a second embodiment of the presentinvention.

[0107]FIG. 11 is a diagram illustrating a packet construction used in adata transmission system according to a third embodiment of the presentinvention.

[0108]FIG. 12 is a diagram illustrating a packet construction used in adata transmission system according to a fourth embodiment of the presentinvention.

[0109]FIG. 13 is a block diagram illustrating a configuration of a datatransmission system according to a fifth embodiment of the presentinvention.

[0110]FIG. 14 is a block diagram illustrating a configuration of aconventional data transmission system.

[0111]FIG. 15 is a block diagram illustrating a configuration of a datatransmission system according to a sixth embodiment of the presentinvention.

[0112]FIG. 16 is a diagram illustrating a packet construction used inthe data transmission system according to the sixth embodiment of thepresent invention.

[0113]FIG. 17 is a diagram illustrating a method of transmittingtransmission data frames in the data transmission system according tothe sixth embodiment of the present invention.

[0114]FIG. 18 is a diagram illustrating a process flow chart of the datatransmission apparatus according to the sixth embodiment of the presentinvention.

[0115]FIG. 19 is a diagram illustrating a process flow chart of the datareception apparatus according to the sixth embodiment of the presentinvention.

[0116]FIG. 20 is a diagram illustrating a packet construction used in adata transmission system according to a seventh embodiment of thepresent invention.

[0117]FIG. 21 is a diagram illustrating a method of transmittingtransmission data frames in the data transmission system according tothe seventh embodiment of the present invention.

[0118]FIG. 22 is a diagram illustrating a method of transmittingtransmission data frames in a data transmission system according to aneighth embodiment of the present invention.

[0119]FIG. 23 is a diagram illustrating a process flow chart of the datatransmission apparatus according to the eighth embodiment of the presentinvention.

[0120]FIG. 24 is a diagram illustrating a process flow chart of the datareception apparatus according to the eighth embodiment of the presentinvention.

[0121]FIG. 25 is a diagram illustrating a method of transmittingtransmission data frames in a data transmission system according to aninth embodiment of the present invention.

BEST MODE TO EXECUTE THE INVENTION EMBODIMENT 1

[0122] A configuration of a data transmission system in a firstembodiment of the present invention is shown in FIG. 1. In FIG. 1,reference numeral 100 denotes a transmission path, and numeral 101denotes a clock control means for controlling a clock of thetransmission path 100. Further, reference numeral 110 denotes atransmission apparatus, and numeral 120 denotes a reception apparatus.The transmission apparatus 110 comprises a data generation means 111, afirst communication control means 112, a data packet generation means113, a transmission-side buffer means 114, and a transmission-sidebuffer control means 115. Further, the reception apparatus 120 comprisesa data processing means 121, a second communication control means 122, adata extraction means 123, a reception-side buffer means 124, and areception-side buffer control means 125, and a clock control means 126.

[0123] In this first embodiment, the transmission data are transmittedin a format defined by IEC60958 from the data generation means 111. FIG.2 is a diagram illustrating an IEC60958 format. As shown in FIG. 2, 1frame is composed of 2 sub-frames in IEC60958 and further, 1 sub-frameis composed of 32 time slots. Then, slots 0 to 3 are for signals forsynchronization discrimination, which are called preambles, and slots 4to 27 are slots allocated for data transmission, on which 24 bits ofdata can be transmitted in 1 sub-frame. Further, slot 28 is for a flagindicating reliability of audio data in the sub-frame (validity flag),slot 29 is for user data which can be freely set by a user, slot 30 isfor a channel status information, and slot 31 is a check bit (paritybit) of 28 bit data length excluding the preamble part.

[0124] The bits of the slots 4 to 31 are subjected to bi-phase markmodulation for dividing 1 slot into 2 symbols for representation, andtransmitted. An example of the bi-phase modulation is shown in FIG. 3.As shown in FIG. 3, a state of the symbol is always inverted at thepoint where a slot changes. Further, in a case where data of the slot is“1”, the state of the symbol is inverted at the center of the slot, andin a case where data of the slot is “0”, the state of the symbol ismaintained. By performing this modulation, DC component of thetransmission line can be minimized and clock reproduction can be easilyperformed.

[0125] Next, the preamble will be described with reference to thedrawings. FIG. 4 is a diagram illustrating a preamble in IEC60958. Thereexist 3 kinds of preambles, that is, preambles X and Y representingchannel 1 and channel 2 respectively and preamble Z representing a headof a block composed of 192 frames. As shown in FIG. 4, a particularpattern which is not represented in bi-phase modulated symbols is usedfor the preamble.

[0126] A data format in the transmission path 100 in this firstembodiment is shown in FIG. 5. In this first embodiment, a format inMedia Oriented Systems Transport (hereinafter referred to as “MOST”)disclosed in Patrick Heck, Hervert Hetzel, Dave Knapp, Kevin Rolfes,Venkat Srinivas, Andreas Stiegler, Tony Susanto, and David Trager. MediaOriented Synchronous Transfer—A Network Protocol for High Quality, LowCost Transfer of Synchronous, Asynchronous, and Control Data on FiberOptic. Presented at the 103rd AES Convention, 1997 September 26-29, NewYork, is used in the transmission path 100. That is, in FIG. 5,reference numeral 501 denotes a preamble in the transmission pathformat, numeral 502 denotes a boundary descriptor, numeral 503 denotes asynchronous data slot, numeral 504 denotes an asynchronous data slot,numeral 505 denotes a control frame, numeral 506 denotes a data forframe control and numeral 507 denotes a parity. Then, the boundarydescriptor 502 indicates a location of a boundary between thesynchronous data slot 503 and the asynchronous data slot 504, and thedata for frame control 506 and the parity 507 are used for frame errordetection and the like. In MOST, the transmission path formats areconsecutively transmitted to the respective apparatuses connected to thetransmission path 100. Then, the respective apparatuses perform datatransmission using the synchronous data slot 503, the asynchronous dataslot 504 or the control frame 505, which are periodically transmittedfrom the transmission path 100.

[0127] In this first embodiment, the transmission data are to betransmitted using the synchronous slot 503. Hereinafter, thetransmission process will be described with reference to the drawings.

[0128]FIG. 6 is a diagram illustrating a process flow chart of thetransmission apparatus in this first embodiment. When the flow starts(step 600), transmission data are input from the data generation means111 to the transmission-side buffer means 114 in the IEC60958 format.The transmission-side buffer control means 115 monitors the accumulateddata amount in the transmission-side buffer means 114, and, when acertain value, for example, 2 frames of data are accumulated, startsdata output from the transmission buffer means 114 to the data packetgeneration means 113 (step 601).

[0129] A read start instruction is outputted to the data packetgeneration means 113 and the data packet generation means 113 transmitsa read signal to the transmission-side buffer means 114, therebyperforming the start of data output (step 602).

[0130] After receiving the first 1 frame of data, the data packetgeneration means 113 performs packetization of the transmission data(step 603). FIG. 7 is a diagram illustrating a packetized format of thetransmission data. Here, FIG. 7(a) shows 1 frame of data beforepacketized and FIG. 7(b) shows packetized data, in which referencenumeral 701 denotes an indicator, numeral 702 denotes a data length,numeral 703 denotes significant data in the packet, and numeral 704denotes spare bits. Further, in figures, numerals described above theformat indicate the number of bits allocated to the respective fields.In this first embodiment, the frame shown in FIG. 7(a) is packetized byomitting bits of preamble and parity as shown in FIG. 7(b) andtransmitted to the transmission path. These preamble and parity bits arerequired at the data processing and are not used during the transmissionbetween the transmission apparatus 110 and the reception apparatus 120via the transmission path 100.

[0131] In FIG. 7(b), the indicator 701 is a flag indicating whether thesignificant data in the packet 703 subsequent thereto start from a headof a block or not, and “1” indicates a case where the data 703 startfrom the head of the block (preamble “Z”) and “0” indicates the othercases. Further, the data length 702 indicates the number of bits of thesignificant data included in the packet. The remaining part is spare bit704.

[0132] The data packet created in the process described above issynchronized with a clock of the transmission path supplied from thefirst communication control means 112 (hereinafter referred to as“transmission path clock”) and is transmitted to the transmission pathwith the output timing of the synchronous channel of the transmissionpath (step 604).

[0133] Then, the data packet generation means 113 stores the accumulateddata amount in the transmission-side buffer means 114 at this time (step605). Then, with the timing of outputting the next synchronous data(step 606), data corresponding to the increased amount from theaccumulated data amount are packetized (step 607) and transmitted to thetransmission path (step 608).

[0134] Then, the number of bits of the spare bit 704 variably changesaccording to the number of bits of the significant data 703 to bepacketized.

[0135] By repeating the operations as described above, the packets arecontinuously transmitted.

[0136]FIG. 8 is a diagram illustrating a process flow chart of thereception apparatus in this first embodiment. When the flow starts (step800), in the reception apparatus 120, the second communication controlmeans 122 receives the data packet and transmits the data packet to thedata extraction means 123 in synchronization with the transmission pathclock (step 801).

[0137] The data extraction means 123 reconstructs the transmission datafrom the packet (adds preamble and parity) (step 802), and transmits thereconstructed data to the reception-side buffer means 124 (step 803).For example, when receiving a packet in which the indicator represents“1”, the data extraction means adds a preamble of “Z” and starts theoutput, and thereafter “Y”, “X”, “Y” . . . are sequentially added aspreambles.

[0138] The reception-side buffer means 124 temporarily accumulates thetransmission data, and starts to output the data to the data processingmeans 121 at the moment when a certain value, for example, 2 frames ofdata are accumulated. The controls for starting the output of thetransmission data, reading and the like are performed by thereception-side buffer control means 125.

[0139] In the reception apparatus 120 in this first embodiment, theclock control means 126 performs processing for controlling an outputclock rate to the data processing means 121 in accordance with theaccumulated data amount in the reception-side buffer means 124. Theclock control means 126 has a clock generating source inside. The clockgenerating source generates an output clock of a value approximate to atransmission data clock which is a clock of the transmission data outputfrom the data generation means 111, and further can slightly adjust therate of the generated output clock since the transmission data clock isreproduced by the reception apparatus 120.

[0140] Hereinafter, the control of the output clock by the clock controlmeans 126 will be described with reference to the drawings. FIG. 9 is adiagram illustrating the clock control method in this first embodiment.FIG. 9(a) shows the accumulated data amount in the reception-side buffermeans 124 wherein the axis of ordinate represents the accumulated dataamounts and the axis of abscissa represents the elapsed time. Further,FIG. 9(b) shows the rates of the clock generated by the clock controlmeans 126 wherein the axis of ordinate represents clock rates and theaxis of abscissa represents the elapsed time.

[0141] The accumulated data amount in the reception-side buffer means124 starts to increase at time t3 (FIG. 9(a)). When the clock controlmeans 126 detects this increase, it increases the rate of the outputclock to be supplied to the buffer control means 125 (FIG. 9(b)). As aresult of increasing the read rate, the increase in the accumulated dataamount stops at time t6 and hence the clock control means 126 stops theprocessing for increasing the output clock rate.

[0142] Then, when the accumulated data amount starts to decrease at timet9, the clock control means 126 reduces the output clock rate. Asdescribed above, by controlling the output clock rate by the clockcontrol means 126, the transmission data are supplied from thereception-side buffer means 124 to the data processing means 121 atalmost the same rate as the rate at which the data generation means 111transmits the transmission data.

[0143] Hereinafter, this first embodiment will be described in moredetails with using a specific example. Here, a system in which while thedata generation means 111 and the clock control means 101 operate on aclock of the same rate in specifications, a synchronization is exactlycaused due to the difference of the clock sources, will be considered,and as an example, a system in which 64 bits of data for 1 frame shownin FIG. 7 are allocated to the synchronous data slot 503 in FIG. 5 inspecifications thus performing the transmission exactly, will beconsidered.

[0144] In a case where the clock sources are precisely identical to eachother, the data packet generation means 113 performs packetization shownin FIG. 7(b), sets 54 bits as the number of bits allocated to the fieldfor the data length 702 and 3 bits as the number of bits allocated tothe field for the spare bit 704 for a packet, and continues to transmitthe packets to the transmission path 100, thereby performing propertransmission.

[0145] However, in a case where a rate at which the data generationmeans 111 transmits the transmission data is lower than a rate of theclock generated by the clock control means 101, when 3 bits are alwaysset as the number of bits of the field for the spare bit 704 in a likemanner and the transmission is performed, the data to be transmitted tothe transmission path 100 become short (underflow). In such a case, thetransmission apparatus of this first embodiment performs processing tosometimes transmit the packet in which the field for the spare bit 704is of 4 bits as well as the packet in which the field for the spare bit704 is of 3 bits, thereby absorbing the clock error.

[0146] Then, in the reception apparatus 120, the transmission data aresequentially input to the reception-side buffer means 124 andtransmitted to the data processing means 121 on the basis of the readsignal of the reception-side buffer control means 125. In a case wherethe rate at which the data generation means 111 transmits thetransmission data is lower than the rate of the clock generated by theclock control means 101, the clock output from the clock control means126 becomes a slightly lower value than the transmission path clock onaverage, that is, becomes equal to the clock on which the datageneration means 111 transmits the transmission data.

[0147] On the other hand, in a case where a rate at which the datageneration means 111 transmits the transmission data is higher than arate of the clock generated by the clock control means 101, when 3 bitsare always set as the number of bits of the field for the spare bit 704in a like manner and the transmission is performed, the data whichcannot be transmitted to the transmission path 100 are graduallyaccumulated in the transmission apparatus 110(overflow). Also in such acase, the transmission apparatus of this first embodiment performsprocessing to sometimes transmit the packet in which the number of bitsof the field for the spare bit 704 is 2 bits as well as the packet inwhich the number of bits of the field for the spare bit 704 is 3 bits,thereby absorbing the clock error.

[0148] Then, in the reception apparatus 120, the transmission data aresequentially input to the reception-side buffer means 124 andtransmitted to the data processing means 121 on the basis of the readsignal of the reception-side buffer control means 125. In a case wherethe rate at which the data generation means 111 transmits thetransmission data is higher than the rate of the clock generated by theclock control means 101, the clock output from the clock control means126 becomes a slightly higher value than the transmission path clock onaverage, that is, becomes equal to the clock on which the datageneration means 111 transmits the transmission data.

[0149] Thus, according to this first embodiment, a data packet obtainedby omitting a preamble or a parity, or both of them, from the datagenerated by the data generation means 111 and adding the data length702 and the spare bit 704 is transmitted as an access unit from thetransmission apparatus 110 to the transmission path 100, and therebydata can be transmitted without shortage or excess by adjusting thelength of the spare bit 704 (the number of bits) even when there is adifference between the clock rate of the transmission path 100, which iscontrolled by the clock control means 101, and the clock rate which isused for the processing inside the transmission apparatus 110, andfurther the reception apparatus 120 reconstructs data by adding to thereceived data the preamble or parity, or both of them, which have beenomitted, and the clock control means 126 adjusts the rate of datareading clock to the reception-side buffer 124 for transmitting data tothe data processing means 121, and thereby the data output from the datageneration means 111 on the side of the transmission apparatus 110 areprocessed at the same rate as the rate at which the data have beenoutput, by the data processing means 121 on the side of the receptionapparatus 120 even when there is a difference between the clock rate ofthe transmission path 100 and the clock rate of the transmissionapparatus 110 and reception apparatus 120.

[0150] Here, while in this first embodiment the indicator 701 represents“1” for the packet starting from a head of a block (a packet of preamble“Z”), the indicator 701 may represent “1” only when the transmissionstarts.

EMBODIMENT 2

[0151] Next, a data transmission system and data transmission methodaccording to a second embodiment of the present invention will bedescribed. This second embodiment is characterized in that a format inpacketization is different from that of the above-described firstembodiment. Hereinafter, a description will be made with reference tothe drawings.

[0152]FIG. 10 is a diagram illustrating a construction of a packet usedin the data transmission system in this second embodiment. In FIG. 10, aframe construction of transmission data shown in FIG. 10(a) is the sameas that shown in the first embodiment. Further, in FIG. 10(b), referencenumeral 1001 denotes an indicator, numeral 1002 denotes a data length,numeral 1003 denotes significant data in the packet, numeral 1004denotes spare bit, and numeral 1005 denotes arbitrary data.

[0153] In this second embodiment, not the number of bits of thesignificant data in the packet 1003 but the number of bits of the sparebit 1004 is described in the field for the data length 1002. Forexample, in a system where while the data generation means 111 and theclock control means 101 operate on a clock of the same rate inspecifications, a synchronization is exactly caused due to the clocksources being different, a difference in the number of bits among therespective transmission frames is slight. That is, the variation in thenumber of bits of the spare bit 1004 ranges between 1 bit and 2 bits andtherefore 2 bits are sufficient for the field for the data length 1002.

[0154] As a result, in this second embodiment, 6 bits of spare portionis generated for 1 frame, and arbitrary data can be written by anapplication in this spare area, that is, the area of the arbitrary data1005.

[0155] Then, a configuration as an apparatus in this second embodimentis identical to that shown in FIG. 1 and the detailed description isomitted here.

[0156] The packet construction of this second embodiment described aboveis effective particularly when synchronizing the clocks in a systemwhere the data generation means 111 and the transmission path operate onclocks of different rates in specifications respectively, for example,in a configuration in which the data generation means 111 whichgenerates data has a clock source of 48 kHz while the clock controlmeans 101 has a clock source of 44.1 kHz. That is, it is necessary thatin such a system, 48/44.1 times the data amount should be transmitted ina packet as compared to a case where the data generation means 111 whichgenerates data has a clock source of 44.1 kHz. Therefore, in such acase, 4 bits among the portion of the arbitrary data 1005 shown in FIG.10 (6 bits) are used for data transmission and the variation in thenumber of bits of the significant data in the packet 1003 is absorbedinto the field for the spare bit 1004 and thereby the transmissionsystem can perform data transmission without failure.

[0157] Thus, according to this second embodiment, with noting that avariation in the number of bits of the spare bit 1004 is slight, thenumber of bits of spare bit 1004 is described in the field for the datalength 1002, and the number of bits thereof is 2 bits, and further thevariation in the number of bits of the significant data in the packet1003 is absorbed using the spare bit 1004 of 2 bits. Therefore, an areafor the arbitrary data 1005 into which an application software can writearbitrary data can be secured in the packet.

EMBODIMENT 3

[0158] Next, a data transmission system and data transmission methodaccording to a third embodiment of the present invention will bedescribed. This third embodiment is characterized in that a format inthe packetization is different from that of the above-described firstembodiment. Hereinafter, description will be made with reference to thedrawings.

[0159]FIG. 11 is a diagram illustrating a construction of a packet usedin the data transmission system in this third embodiment. In FIG. 11, aframe construction of transmission data shown in FIG. 11(a) is the sameas that shown in the first embodiment. Further, in FIG. 11(b), referencenumeral 1101 denotes a spare bit length, numeral 1102 denotes a preambletype, numeral 1103 denotes a preamble location pointer, numeral 1104denotes significant data in the packet, and numeral 1105 denotes sparebit.

[0160] This third embodiment is effective especially when theinformation for the frame reconstruction is periodically notified to thereception apparatus 120 so as to achieve the synchronization of thesystem in such a system that while the data generation means 111 and theclock control means 101 in FIG. 1 operate on the clock of the same ratein specifications, a synchronization is exactly caused due to thedifference of the clock sources.

[0161] Here, while the frame information is periodically transmittedalso by the above-described first embodiment, the indicator 701represents only that the significant data in the packet 703 subsequentthereto start from a head of a block or the other case (refer to FIG.7(b)), in the first embodiment. Therefore, for example, in a case wherea stream gets discontinued halfway, frames cannot be reconstructed untila packet including an indicator 701 indicating that significant datastart from a head of a block is received next. Then, in this thirdembodiment, a preamble type of the significant data in the packet or thelike is added to each packet to facilitate the frame reconstruction.

[0162] Then, a configuration as an apparatus of this third embodiment isidentical to that shown in FIG. 1, and the detailed description isomitted here.

[0163] The significant data 1104 and spare bit 1105 for 1 packet in thisthird embodiment are of 55 bits in total. The number of bits allocatedto the field for the spare bit 1105 is indicated by the spare bit length1101 of 2 bits.

[0164] Here, in a case where there is no a synchronization in clockbetween the data generation means 111 and the clock control means 101,the timing for 1 frame always coincide with that for 1 packet, and thesignificant data 1104 is always of 54 bits and the spare bit 1105 isalways of 1 bit. On the other hand, in a case where there is asynchronization in clock between the data generation means 111 and theclock control means 101, a value which is indicated in the spare bitlength 1101 is set to 0 or 2, thereby performing adjustment. Thisadjustment is performed in a manner similar to that shown in theabove-described second embodiment.

[0165] The preamble location pointer 1103 is of 5 bits, indicating wherea break of the sub-frame is located in the significant data in thepacket 1104. Since the significant data of a sub-frame is always of 27bits (FIG. 11(a)), the break of the sub-frame is present anywhere withinthe first 27 bits in the significant data in the packet 1104. Thepreamble location pointer 1103 indicates the number of bits of up to thefirst break of the sub-frame.

[0166] The preamble type 1102 is of 2 bits in which the preamble type ofthe sub-frame starting from the break indicated by the above-describedpreamble location pointer 1103 is described.

[0167] As shown in FIG. 2, 3 types of preambles, Z, X and Y, arepresent, and the preambles are “Z” “Y” “X” “Y” . . . from the head of 1block. That is, in cases where the preamble is Z and the preamble is X,the preamble of the subsequent sub-frame is Y while in a case where thepreamble is Y, there are 2 case, i.e., a case where the preamble of thesubsequent sub-frame is Z and a case where it is X. Then, in the casewhere the preamble is Y in the preamble type 1102, different symbols areallocated between in the case where the preamble of the subsequentsub-frame is Z and in the case where it is X.

[0168] For example, in a case where the first preamble in the packet isZ, “00” is allocated, in a case where the first preamble in the packetis X, “01” is allocated, and in a case where the first preamble is Y andthe preamble of the subsequent sub-frame is z, “10” is allocated, and ina case where the first preamble is Y and the preamble of the subsequentsub-frame is X, “11” is allocated.

[0169] Then, the information in the preamble location pointer 1103 andthe preamble type 1102 are reflected in the frame reconstruction by thereception apparatus 120.

[0170] As described above, according to this third embodiment, since thepreamble location pointer 1103 is described in the field for thearbitrary data 1005 which is reserved in the second embodiment (FIG.10(b)), when the reception apparatus 120 reconstructs the frame, thereception apparatus 120 can receive the information on the location andtype of the preamble from the transmission apparatus 110. For example,even when the stream gets discontinued, the reception apparatus 120 caneasily realize the frame reconstruction, thereby enhancing thereliability of the system.

[0171] Then, while in this third embodiment the number of bits of thespare bit 1105 is indicated in the field indicating the data length ofthe transmitted packet, for example, the number of bits of thesignificant data in the packet may be indicated as shown in theabove-described first embodiment instead of the number of bits of sparebits, depending on the number of bits which can be transmitted for eachpacket.

EMBODIMENT 4

[0172] Next, a data transmission system and data transmission methodaccording to a fourth embodiment of the present invention will bedescribed. This fourth embodiment is characterized in that a format inthe packetization is different from that of the above-described firstembodiment. Hereinafter, a description will be made with reference tothe drawings.

[0173]FIG. 12 is a diagram illustrating a packet construction used inthe data transmission system in this fourth embodiment. In FIG. 12, theframe construction of the transmission data shown in FIG. 12(a) is thesame as that shown in the first embodiment. Further, in FIG. 12(b),reference numeral 1201 denotes a frame head indicator, numeral 1202denotes a preamble type, numeral 1203 denotes a spare bit indicator,numeral 1204 denotes significant data in the packet, and numeral 1205denotes spare bit.

[0174] The configuration of this fourth embodiment is effectiveespecially when the information for frame reconstruction is periodicallynotified to the reception apparatus 120 so as to achieve synchronizationof the system in such a system that the data generation means 111 andthe transmission path operate respectively on the clocks of thedifferent rates in specifications, for example, in such a configurationthat the data generation means 111 which generates data has a clocksource of 48 kHz while the clock control means 101 has a clock source of44.1 kHz.

[0175] Then, a configuration as an apparatus of this fourth embodimentis identical to that shown in FIG. 1, and the detailed description isomitted here.

[0176] The significant data 1204 and the spare bit 1205 for one packetin this fourth embodiment are of 60 bits in total. The length of thespare bit 1205 is 0 bit or 6 bits, which is discriminated by the sparebit indicator 1203.

[0177] In this fourth embodiment, in the packet construction in thetransmission apparatus 110, in a case where the field for thesignificant data in the packet 1204 starts at a break of a sub-frame,the frame head indicator 1201 is set to “1”. Further, at this time, thetype of the sub-frame starting from the frame head is described usingthe preamble type (2 bits) 1202. On the other hand, in a case where thebreak of the sub-frame is located at a location other than the head ofthe packet, the frame head indicator 1201 is set to “0”.

[0178] The reception apparatus 120 reflects the frame head indicator1201 and the preamble type 1202 in the frame reconstruction.

[0179] As described above, according to this fourth embodiment, theconstruction is such that the spare bit 1205 is provided in the packetto absorb the variation in the number of bits and the frame headindicator 1201 indicating the head of the frame is provided in thepacket, and therefore, when the reception apparatus 120 reconstructs theframe, it can periodically receive the information on the location andtype of the preamble, and the reception apparatus 120 can easily realizeframe reconstruction, for example, even when the stream getsdiscontinued, thereby enhancing the reliability of the system.

[0180] Then, while in this fourth embodiment the number of bits of sparebit 1205 is indicated in the field indicating the data length of thetransmitted packet, for example, the number of bits of the significantdata in the packet may be indicated as shown in the above-describedfirst embodiment instead of the number of bits of spare bit, dependingon the number of bits which can be transmitted for each packet.

EMBODIMENT 5

[0181] Next, a data transmission system and data transmission methodaccording to a fifth embodiment of the present invention will bedescribed. This fifth embodiment is different from the above-describedsecond embodiment in that the area of the arbitrary data 1005 shown inthe second embodiment (FIG. 10(b)) is used for time-informationtransmission for synchronizing the transmission and reception.Hereinafter, a description will be made with reference to the drawings.

[0182]FIG. 13 is a diagram illustrating a configuration of the datatransmission system in this fifth embodiment, and in FIG. 13, the samereference numerals as those of FIG. 1 denote the same or correspondingparts, and reference numeral 1310 denotes a transmission apparatus,numeral 1313 denotes a data packet generation means, numeral 1314denotes a transmission-side buffer means, numeral 1315 denotes atransmission-side buffer control means, numeral 1316 denotes atransmission data clock extraction means, and numeral 1317 denotes atime-information generation means.

[0183] Further, reference numeral 1320 denotes a reception apparatus,numeral 1323 denotes a data extraction means, numeral 1324 denotes areception-side buffer means, numeral 1325 denotes a reception-sidebuffer control means and numeral 1326 denotes a clock control means.

[0184] Hereinafter, the description will be made with emphasis on thecharacteristic operation of the present invention. In the transmissionapparatus 1310 of this fifth embodiment, the transmission data inputfrom the data generation means 111 are also input to the transmissiondata clock extraction means 1316, in which the extraction of thetransmission data clock which is the clock of the transmission dataoutput from the data generation means 111 is performed. The transmissiondata clock extracted by the transmission data clock extraction means1316 is transmitted to the time-information generation means 1317. Thistime-information generation means 1317 has a timer for generatingtime-information, and generates time-information by operating the timerwith using the extracted transmission data clock.

[0185] The data packet generation means 1313 reads time-information fromthe time-information generation means 1317 in synchronization with thetiming of transmitting a packet, and writes the time at the transmissiontiming in the field for the arbitrary data 1005 in FIG. 10.

[0186] On the other hand, in the reception apparatus 1320, the dataextraction means 1323 receives the packet including thetime-information, extracts the time-information from the packet, andtransmits the time-information to the clock control means 1326.

[0187] The clock control means 1326 has a clock generating sourceinside. The clock generating source generates an output clock of a valueapproximate to the transmission data clock, and can slightly adjust therate of the output clock generated since the transmission data clock isreproduced in the reception apparatus 1320. The clock control means 1326sequentially compares the time-information created on the basis of thereceived transmission data clock and the time calculated from the outputclock from the clock generating source, and adjusts the rate of theoutput clock so that the time-information and the time coincide witheach other. This operation allows the clock of the transmission dataextracted by the transmission apparatus 1310 and the output clock whichis output by the clock control means 1326 in the reception apparatus1320 to be synchronized with each other achieving synchronization of thesystem.

[0188] In this way, according to this fifth embodiment, thetime-information generation means 1317 is provided in the transmissionapparatus 1310, and the time-information at the data transmission timingis described in the field for the arbitrary data 1005. The dataextraction means 1323 in the reception apparatus 1320 extracts thetime-information, and the clock control means 1326 compares theextracted time-information and the time-information based on the outputclock generated from the clock generating source inside the clockcontrol means 1326, and the clock control means 1326 adjusts the clockon the side of the reception apparatus 1320 so that both of themcoincide with each other, thereby achieving synchronization between thetransmission apparatus 1310 and the reception apparatus 1320 in thesystem.

[0189] Then, while in this fifth embodiment the transmission data clockis extracted from the transmission data, for example, the presentinvention is applicable exactly in a like manner even in a system inwhich the transmission clock is input separately from the transmissiondata.

[0190] Further, while in this fifth embodiment the time-information istransmitted for every packet, the transmission for every packet is notnecessarily required. For example, the time-information may betransmitted for every several packets and in packets in which notime-information is transmitted, the arbitrary data 1005 can be used foranother purpose, for example, for the same purpose as the spare bitswhich are shown in the first embodiment.

[0191] Further, while in this fifth embodiment the number of bits ofspare bit 1004 is indicated in the field indicating the data length ofthe transmitted packet, the number of bits of the significant data inthe packet may be, for example, indicated instead of the number of bitsof spare bits, depending on the number of bits which can be transmittedfor each packet as shown in the first embodiment.

EMBODIMENT 6

[0192] Next, a data transmission system and data transmission methodaccording to this sixth embodiment will be described. While in each ofthe above-described embodiments, cases where the clock source of thedata generation means 111 is different from the clock source of thetransmission path clock are described, described in this sixthembodiment will be a case where while a clock of the transmission datagenerated by the data generation means 111 (hereinafter referred to as“transmission data clock”) is different in rate from the transmissionpath clock in specifications, clock sources thereof are the same.Hereinafter, a description will be made with reference to the drawings.

[0193]FIG. 15 is a diagram illustrating a configuration of the datatransmission system in this first embodiment. In FIG. 15, the samereference numerals as those in FIG. 1 denote the same or correspondingparts, and reference numeral 1501 denotes a clock control means, numeral1510 denotes a transmission apparatus, numeral 1511 denotes a datageneration means, and numeral 1512 denotes a first communication controlmeans. Further, reference numeral 1520 denotes a reception apparatus,numeral 1522 denotes a second communication control means, numeral 1524denotes a reception-side buffer means, numeral 1525 denotes areception-side buffer control means, and numeral 1527 denotes a secondclock control means.

[0194] Hereinafter, a description will be made with emphasis on thecharacteristic operation of the present invention. In the transmissionapparatus 1510 of this sixth embodiment, the first clock control means1501 generates the transmission path clock on the basis of thetransmission data clock, and transmits the transmission path clock tothe first communication control means 1512.

[0195] Then, the transmission path 100 operates in synchronization withthe transmission data clock which is input to the first communicationcontrol means 1512.

[0196] On the other hand, in the reception apparatus 1520, the secondcommunication control means 1522 inputs the transmission path clockobtained from the transmission path 100 to the second clock controlmeans 1527. The second clock control means 1527 generates thetransmission data clock from the transmission path clock and suppliesthe transmission data clock to the reception-side buffer control means1525. The reception-side buffer control means 1525 controls the datareading from the reception-side buffer means 1524 using the transmissiondata clock. In this way, in this sixth embodiment, the clock source ofthe transmission apparatus 1510 is supplied from the data generationmeans 1511 to generate the transmission path clock, and the receptionapparatus 1520 reproduces the transmission data clock on the side of thetransmission apparatus using the reverse process, thereby supplying thesame transmission data clock to the transmission apparatus 1510 and thereception apparatus 1520 and achieving synchronization between bothapparatuses, that is, synchronization of the system.

[0197] Hereinafter, the packetization of the transmission data frame inthis sixth embodiment will be described using the drawings. FIG. 16 is adiagram illustrating a packet construction used in the data transmissionsystem of this sixth embodiment. In FIG. 16, a frame construction of thetransmission data shown in FIG. 16(a) is the same as that shown in thefirst embodiment. Further, in FIG. 16(b), reference numeral 1601 denotesa preamble type, and numeral 1602 denotes significant data in thepacket. In this sixth embodiment, as in the above-described firstembodiment, 54 bits of significant data are made into 1 packet, and 2bits of preamble type are added thereto.

[0198] Next, a method of transmitting packetized transmission dataframes in this sixth embodiment will be described using FIG. 17. Then,in this sixth embodiment, the transmission data clock is based on 48 kHzand 64 bits (that is, 1 frame) are transmitted in {fraction (1/48000)}second. Further, the transmission path clock is based on 44.1 kHz and atransmission path frame for transmitting 64 bits in {fraction (1/44100)}second is reserved.

[0199] The transmission system in this sixth embodiment generates atransmission path clock using a transmission data clock. Synchronizationrelationship is established between the transmission data clock and thetransmission path clock, and the synchronization relationship that while160 transmission data frames (transmitting 64 bits in {fraction(1/48000)} second) are input, 147 transmission path frames aretransmitted, is established. Therefore, 160 transmission data frames aretransmitted using 147 transmission path frames, thereby establishingproper synchronization relationship.

[0200] To be specific, in this sixth embodiment, bits for a preamble anda parity are omitted from the frame shown in FIG. 16(a) and the preambletype 1601 is added as shown in FIG. 16(b), thereby forming atransmission data frame of 64 bits into a packet of 56 bits. Thus, thedata amount for 160 frames is 160×56=8960 bits. The number of framesrequired for transmitting these using transmission path frames is8960/64=140 frames, and the transmission can be made in a state where147−140=7 frames are spared.

[0201] The transmission data frames each of which has been thuspacketized as 56 bits (FIG. 17(c)) are sequentially combined (FIG.17(b)) and are then transmitted 64 bits by 64 bits using thetransmission path frame (FIG. 17(a)). In FIG. 17, the transmission dataframes 1,2 . . . are transmitted in the transmission path frames 8,9 . .. respectively in this order, and the transmission of a total of 8960bits of up to transmission path frame 147, that is, 160 transmissiondata frames is completed. By repeating these, the transmission dataframes are continuously transmitted to the side of the receptionapparatus 1520.

[0202] Then, in this sixth embodiment, data for packet synchronizationbetween the transmission apparatus 1510 and the reception apparatus 1520are accommodated in the transmission path frames 1 to 7 which have notbeen used for the transmission of transmission data frames. For example,in the transmission apparatus 1510, all the data of the transmissionpath frame 1 are set to “1”, and the reception apparatus 1520 identifiesas the transmission path frame 1 the transmission path frame in whichall the data are set to “1” at the time of detecting the transmissionpath frame, and recognizes that a data packet starts from thetransmission path frame 8 which is the seventh frame from thetransmission path frame 1.

[0203] At this time, if the allocation to the preamble type 1601 isother than “11”, for example, “00” is allocated for preamble Z, “01” forpreamble X and “10” for preamble Y, each of the transmission path framesincluding packets, that is, the transmission path frames 8 to 147 surelyincludes a bit of “0”, thereby preventing the transmission path framesincluding packet synchronization data from being erroneously identified.Then, the arbitrary data, for example, the music data in the case oftransmitting audio data, and the like, may be accommodated in thetransmission path frames 2 to 7, which are other than the transmissionpath frame 1 used for the transmission of the synchronization data,among the transmission path data frames 1 to 7 which do not include thetransmission data frames, and transmitted.

[0204] Hereinafter, the transmission process will be described withreference to the drawings. FIG. 18 is a diagram illustrating a processflow chart of the transmission apparatus in this sixth embodiment. Whenthe flow starts (step 1800), the transmission data are input from thedata generation means 1511 to the transmission-side buffer means 114.The transmission-side buffer control means 115 monitors the accumulateddata amount in the transmission-side buffer means 114 and, when acertain value, for example, 2 frames of data are accumulated (step1801), starts process of data output to the data packet generation means1513 (step 1802). That is, the data packet generation means 1513initially transmits the transmission path frames 1 to 7 insynchronization with the timing of the transmission path clock. Then,the data packet generation means 1513 reads 1 frame of data from thetransmission-side buffer means 114 and performs the packetization shownin FIG. 16 (step 1804). Then, when the data packet generation means 1513does not hold data for 1 transmission path frame, that is, 64 bits ofdata in this sixth embodiment, which are to be transmitted subsequently(step 1805), the process is returned to step 1804, and 1 frame oftransmission data are read from the transmission-side buffer means 114and packetized.

[0205] Then, when the timing of outputting data to the transmission pathframe comes (step 1806), data of 1 transmission path frame, that is, 64bits of data in this six embodiment, are output to the transmission path(step 1807). Then, processes of step 1805 to step 1807 are repeateduntil the data packet generation means 1513 outputs the transmissionpath frame 147 in FIG. 17, and the output of the transmission path frame147 is completed (step 1808), and then the processes of step 1803 tostep 1809 are repeated. Thereby, the packets are continuouslytransmitted.

[0206]FIG. 19 is a diagram illustrating a process flow chart of thereception apparatus in this six embodiment. When the flow starts (step1900), the reception apparatus 1520 receives the transmission pathframes (step 1901) and, when the data of the transmission path frameindicates a frame including synchronization data indicating transmissionpath frame 1 (step 1902), starts the process (step 1903). Subsequently,the data extraction means 1523 receives transmission path frame 2 totransmission path frame 7 subsequent to the transmission path frame 1(step 1904), and the data extraction means 1523 subsequently receivesthe transmission path frames (step 1905). Then, the data extractionmeans 1523 processes data for transmission data frame from the receivedtransmission path frames, reconstructs the sub-frames, and outputs thesub-frames to the reception-side buffer means 1524 (step 1906). Then,processes of step 1905 to step 1906 are repeated until the transmissionpath frame 147 in FIG. 17 is received, and the process of transmissionpath frame 147 is completed (step 1907), and then processes of step 1901to step 1908 are repeated.

[0207] Data accumulated in the reception-side buffer 1524 are read withthe same clock as the transmission data clock in the transmissionapparatus 1510 and transmitted to the data processing means 121.

[0208] In this way, according to this sixth embodiment, in a case wherewhile the clock source of the data generation means 1511 and the clocksource of the transmission path 100 are the same, the clock rate of thetransmission data output from the data generation means 1511 isdifferent from the clock rate of the transmission path 100, that is, ina system operating based on the transmission data clock of 48 kHz andthe transmission path clock of 44.1 kHz, the transmission apparatus 1510creates the transmission path clock from the transmission data clock inthe first clock control means 1501, packetizes frames of thetransmission data as 56 bits, and sequentially combines the packetizedframes, and thereafter transmits the frames 64 bits by 64 bits withusing the transmission path frame, and the reception apparatus 1520receives the transmission path frame and the transmission path clock andcreates the transmission data clock from the transmission path clock inthe second clock control means 1527, and outputs the transmission datato the data processing means 121 on the basis of the transmission dataclock, and therefore the synchronized transmission between thetransmission apparatus 1510 and the reception apparatus 1520 can berealized.

[0209] Then, while in this sixth embodiment the transmission data clockis output from the data generation means 1511 to the transmissionapparatus 1510 and the first clock control means 1501 generates thetransmission path clock from the data transmission clock, anyconfiguration may be adopted as long as the configuration is one inwhich the transmission data clock and the transmission path clock aregenerated from the same clock source. For example, the configuration maybe one in which the first clock control means 1501 exists in anotherapparatus on the transmission path 100, and in this case, the datageneration means 1511 receives the transmission path clock generated bythe first clock control means 1501 in the other apparatus, and createsthe transmission data clock from the received transmission path clock.

[0210] Further, while in this sixth embodiment each of 64 bits of thetransmission path frame 1 accommodates “1”, it is not necessarilyrestricted to this value. For example, a frame other than thetransmission path frame 1 may be for synchronization data, or aplurality of frames may be used for synchronization data. Further, onlyone or more bits of the frame may be used as a mark for the transmissionpath frame including synchronization data, and the other bits may beused for another purpose, for example, for arbitrary data. Further,while in this sixth embodiment a system operating based on thetransmission data frame of 48 kHz and the transmission path frame of44.1 kHz is shown, they are not restricted to these numeric values, andany system is applicable by changing the number of transmission dataframes and the number of the transmission path frames as long as thesystem is one in which the clock sources of the transmission data frameand the transmission path frame are common. For example, in a systemoperating based on the transmission data frame of 44.1 kHz and thetransmission path frame of 48 kHz, the synchronization relationship thatwhile 147 transmission data frames are input, 160 transmission pathframes are transmitted, is established, and therefore in a case wherepacketization is performed on the basis of the method in this sixthembodiment and 56 bits of data are transmitted in 1 transmission pathframe, when the transmission path for transmitting 56 bits in {fraction(1/48000)} second is reserved, data can be transmitted using 147transmission path frames and the remaining 13 transmission path framescan be used for the transmission of synchronization data and thetransmission of arbitrary data.

EMBODIMENT 7

[0211] Next, a data transmission system and data transmission methodaccording to this seventh embodiment will be described. This seventhembodiment is characterized in that a format in packetization and amethod of transmission to the transmission path are different from thosefor the above-described sixth embodiment. Hereinafter, a descriptionwill be made with reference to the drawings. Then, an apparatusconfiguration in this seventh embodiment is similar to that shown inFIG. 15, and the detailed description will be omitted here.

[0212]FIG. 20 is a diagram illustrating a packetization of thetransmission data frame in this seventh embodiment. In FIG. 20, thetransmission data frame construction shown in FIG. 20(a) is the same asthat shown in the first embodiment. Further, in FIG. 20(b), referencenumeral 2001 denotes significant data in the packet. In this seventhembodiment, only the significant data of the transmission data frame areextracted and packetized.

[0213] A method of transmitting the packetized transmission data framesin this seventh embodiment is shown in FIG. 21. Then, the relationshipbetween the transmission data clock and the transmission path frameclock in this seventh embodiment is the same as that in the case of theabove-described sixth embodiment, and the relationship between thetransmission data frame and the transmission path frame is similar tothe relationship in the above-described sixth embodiment. That is, 160transmission data frames are transmitted using 147 transmission pathframes, thereby establishing proper synchronization relationship.

[0214] In this seventh embodiment, as shown in FIG. 20(b), atransmission data frame of 64 bits is formed into a packet of 54 bits.Thereby, the data amount for 160 frames are 160×54=8640 bits. The numberof frames required for transmitting these using the transmission pathframe is 8640/64=135 frames, and in this seventh embodiment, thetransmission can be made in a state where 147−135=12 frames are spared.

[0215] The transmission data frames each of which has been thuspacketized as 54 bits (FIG. 21(c)) are sequentially combined (FIG.21(b)) and thereafter are transmitted 64 bits by 64 bits using thetransmission path frames (FIG. 21(a)). In FIG. 21, the transmission dataframes 1, 2 . . . are transmitted in the transmission path frames 13, 14. . . respectively in this order, and the transmission of a total of8640 bits of up to transmission path frame 147, that is, 160transmission data frames is completed. By repeating these, thetransmission data frames are continuously transmitted to the side of thereception apparatus 1520.

[0216] Then, in this seventh embodiment, any of the transmission pathframes 1 to 12 which have not been used for the transmission of thetransmission data frames, or some frames thereof are used to synchronizethe transmission apparatus 1510 and the reception apparatus 1520 inreceiving packets. For example, the synchronization data 2002 inwhich-each of 64 bits is set to “0” are accommodated in the transmissionpath frame 12 and when the reception apparatus 1520 detects thetransmission path frame 12 including the synchronization data 2002 inwhich each of 64 bits is set to “0”, the reception apparatus 1520recognizes that a data packet starts from the subsequent frame.

[0217] Further, as another example, data to be accommodated in each of64 bits of the transmission path frame 11 is 1 and data to beaccommodated in each of 64 bits of the transmission path frame 12 is 0,and the reception apparatus 1520 recognizes that a data packet startsfrom a frame detected subsequent to the transmission path frame 11 inwhich each of 64 bits is set to “1” and the transmission path frame 12in which each of 64 bits is set to “0”.

[0218] In this way, according to this seventh embodiment, in a casewhere while the clock source of the data generation means 1511 and theclock source of the transmission path 100 are the same, the clock rateof the transmission data output from the data generation means 1511 isdifferent from the clock rate of the transmission path 100, that is, ina system operating based on the transmission data frame of 48 kHz andthe transmission path clock of 44.1 kHz, the transmission apparatus 1510creates the transmission path clock from the transmission data clock inthe first clock control means 1501, packetizes the frame of thetransmission data as 54 bits, and sequentially combines the packetizedframes, and thereafter transmits the frames 64 bits by 64 bits usingtransmission path frame, and the reception apparatus 1520 receives thetransmission path frame and the transmission path clock and creates thetransmission data clock from the transmission path clock in the secondclock control means 1527, and outputs the transmission data to the dataprocessing means 121 on the basis of the transmission data clock, andtherefore the synchronized transmission between the transmissionapparatus 1510 and the reception apparatus 1520 can be realized.

[0219] Then, while in this seventh embodiment the transmission dataclock is output from the data generation means to the transmissionapparatus and the first clock control means generates the transmissionpath clock from the transmission data clock, any configuration may beadopted as long as the configuration is one in which the transmissiondata clock and the transmission path clock are generated from the sameclock source as in the above-described sixth embodiment.

[0220] Further, a method of packet reception synchronization in thisseventh embodiment is an example, and the method is not necessarilyrestricted thereto. For example, frames other than frames used forsynchronization among the transmission path frames 1 to 12 may be usedfor the arbitrary data transmission and the like.

[0221] Further, while in this seventh embodiment a system operatingbased on the transmission data frame of 48 kHz and based on thetransmission path frame of 44.1 kHz is shown, they are not restricted tothese numeric values, and any system is applicable by changing thenumber of transmission data frames and the number of transmission pathframes as long as the system is one in which the clock sources of thetransmission data frame and the transmission path frame are common.

EMBODIMENT 8

[0222] Next, a data transmission system and data transmission methodaccording to this eighth embodiment will be described. While in each ofthe above-described embodiments, the system and method in which thetransmission apparatus omits data which need not be transmitted usingthe transmission path, among the transmission data, to generate datapacket performing transmission are described, described in this eighthembodiment will be a case where when while the clock of the transmissiondata is different in rate from the clock of the transmission path inspecifications, the clock sources are the same, all the bits of thetransmission data are transmitted without omitting unnecessary data.Hereinafter, a description will be made with reference to the drawings.Then, an apparatus configuration in this eighth embodiment is similar tothat shown in FIG. 15, and a detailed description is omitted here.

[0223]FIG. 22 is a diagram illustrating a method of transmittingtransmission data frames in this eighth embodiment. Then, in this eighthembodiment, the transmission data clock is based on 48 kHz and 64 bits(that is, 1 frame) are transmitted in {fraction (1/48000)} second.Further, the transmission path clock is based on 44.1 kHz and atransmission path frame for transmitting 72 bits in {fraction (1/44100)}second is reserved.

[0224] In a transmission system of this eighth embodiment, omission ofdata included in the transmission data is not performed unlike in thecases of the respective embodiments described above. Further, atransmission path clock is generated using a transmission data clock.Then, in this eighth embodiment, the transmission path clock is based on48 kHz and the transmission data clock is based on 44.1 kHz, and thetransmission path clock is faster than the transmission data clock, andtherefore it is necessary that the transmission path frame should bemade larger than the transmission data frame. Further, in thetransmission system of this eighth embodiment, the synchronizationrelationship similar to those shown in the above-described sixth andseventh embodiments is established and 160 transmission data frames aretransmitted using 147 transmission path frames, thereby establishingproper synchronization relationship.

[0225] To be specific, in this eighth embodiment, the transmission dataframe of 64 bits obtained by omitting nothing, which is shown in FIG.22(c), is transmitted. Thereby, the data amount for 160 frames are160×64=10240 bits. The number of frames required for transmitting theseusing the transmission path frame is 10240/72=142.22 . . . , andtherefore the transmission data for 160 frames can be transmitted byusing 143 transmission path frames.

[0226] The transmission data frames each of which has been thus obtainedby packetizing all the transmission data as 64 bits (FIG. 22(c)) aresequentially combined (FIG. 22(b)), and thereafter are transmitted 72bits by 72 bits using transmission path frames (FIG. 22(a)). In FIG. 22,the transmission data frames 1, 2, . . . are transmitted in thetransmission path frames 5, 6, . . . respectively in this order, and thetransmission of a total of 10240 bits of up to the transmission pathframe 147, that is, 160 transmission frames is completed. Then, thesignificant data 2202 of 10240−72×142=16 bits are transmitted in thelast transmission path frame 147, and the remaining 56 bits areinsignificant data 2203 (refer to FIG. 22(a) and FIG. 22(b)). Byrepeating these, the transmission data frames are continuouslytransmitted to the side of the reception apparatus 1520.

[0227] Then, in this eighth embodiment, the data for packetsynchronization between the transmission apparatus 1510 and thereception apparatus 1520 are accommodated in the transmission pathframes 1 to 4 which have not been used for the transmission of thetransmission data frames. For example, in the transmission apparatus1510, all the data of the transmission path frame 1 are set to “1”, andthe reception apparatus 1520 identifies the transmission path frame inwhich all the data are set to “1” as the transmission path frame 1 atthe time of detecting the transmission path frame, and recognizes that adata packet starts from the transmission path frame 5 which is thefourth frame from the transmission path frame 1.

[0228] Then, the arbitrary data, for example, user data, or music datain the case of transmitting audio data as significant data, may beaccommodated in the transmission path frames 2 to 4 and transmitted.

[0229] Hereinafter, the transmission process will be described withreference to the drawings. FIG. 23 is a diagram illustrating a processflow chart of the transmission apparatus in this eighth embodiment. Whenthe flow starts (step 2300), the transmission data are input from thedata generation means 1511 to the transmission-side buffer means 114.The transmission-side buffer control means 115 monitors the accumulateddata amount in the transmission-side buffer means 114 and, when acertain value, for example, 2 frames of data are accumulated (step2301), instructs the data packet generation means 1513 to start dataoutput (step 2302). That is, the data packet generation means 1513initially transmits the transmission path frames 1 to 4 insynchronization with the timing of the transmission path clock. Then,the data packet generation means 1513 reads 1 frame of data from thetransmission-side buffer means (step 2304). Then, when the data packetgeneration means 1513 does not hold data for 1 transmission path frame,that is, data of 72 bits in this eighth embodiment, which are to besubsequently transmitted (step 2305), the process returns to step 2304,and 1 frame of transmission data are read from the transmission-sidebuffer means 114.

[0230] Then, when the timing of outputting data to the transmission pathframe comes (step 2306), 1 transmission path frame of data, that is, 72bits of data in this eighth embodiment, are output to the transmissionpath (step 2307). Then, processes of step 2305 to step 2307 are repeateduntil the data packet generation means 1513 outputs the transmissionpath frame 146 in FIG. 22, and when the timing of outputting data to thetransmission path frame comes(step 2310), the insignificant data of 56bits are added to the last 16 bits of data in the transmission dataframe 160 and the resultant is transmitted as the transmission pathframe 147 (step 2311). Then, the output of the transmission path frame147 is completed, and then the processes of step 2303 to step 2311 arerepeated. Thereby, packets are continuously transmitted.

[0231]FIG. 24 is a diagram illustrating a process flow chart of thereception apparatus in this eighth embodiment. When the flow starts(step 2400), the reception apparatus 1520 receives the transmission pathframe (step 2401), and when the data of the transmission path frameinclude synchronization data indicating transmission path frame 1 (step2402), the process is started (step 2403). Subsequently, the dataextraction means 1523 receives the transmission path frame 2 totransmission path frame 4 subsequent to the transmission path frame 1(step 2404), and the data extraction means 1523 subsequently receivesthe transmission path frame (step 2405). Then, the data extraction means1523 reconstructs the transmission data frame from the receivedtransmission path frame, and outputs the reconstructed frame to thereception-side buffer means 1524 (step 2406). Then, processes of step2405 to step 2406 are repeated until the transmission path frame 147 inFIG. 22 is received, and the process of the transmission path frame 147is completed (step 2407), and then processes of step 2401 to step 2408are repeated. Then, the insignificant bits 2203 which have been added bythe transmission apparatus 1510 are discarded from the transmission pathframe 147 (refer to FIG. 22(a)).

[0232] Then, data accumulated in the reception-side buffer 15243 areread with the same clock as the transmission data clock in thetransmission apparatus 1510, and are transmitted to the data processingmeans 121.

[0233] In this way, according to this eighth embodiment, in a case wherewhile the clock source of the data generation means 1511 and the clocksource of the transmission path 100 are the same, the clock rate of thetransmission data output from the data generation means 1511 isdifferent from the clock rate of the transmission path 100, that is, ina system operating based on the transmission data clock of 48 kHz andthe transmission path clock of 44.1 kHz, the transmission apparatus 1510creates the transmission path clock from the transmission data clock inthe first clock control means 1501, and sequentially combines thetransmission data frames and thereafter transmits the frames 72 bits by72 bits with using the transmission path frame, and the receptionapparatus 1520 receives the transmission path frame and the transmissionpath clock and creates the transmission data clock from the transmissionpath clock in the second clock control means 1527, and outputs thetransmission data to the data processing means 121 on the basis of thetransmission data clock, and therefore the synchronized transmissionbetween the transmission apparatus 1510 and the reception apparatus 1520can be realized. Further, in this eighth embodiment, since thetransmission data are not omitted and all the data are transmitted, theprocesses in the data packet generation means 1513 on the side of thetransmission apparatus 1510, or the processes in the data extractionmeans 1523 on the side of the reception apparatus 1520 are reduced.

[0234] Then, while in this eighth embodiment the transmission data clockis output from the data generation means 1511 to the transmissionapparatus 1510 and the first clock control means 1501 generates thetransmission path clock, any configuration may be adopted as long as theconfiguration is one in which the transmission data clock and thetransmission path clock are generated from the same clock source. Forexample, the configuration may be one in which the first clock controlmeans 1501 exists in another apparatus on the transmission path 100, andin this case, the data generation means 1511 receives the transmissionpath clock generated by the first clock control means 1501 in the otherapparatus, and generates the transmission data clock from the receivedtransmission path clock.

[0235] Further, while in this eighth embodiment each of 64 bits of thetransmission path frame 1 accommodates “1”, it is not necessarilyrestricted to this value. For example, a frame other than thetransmission path frame 1 may be for synchronization, or a plurality offrames may be used for synchronization. Further, only one or more bitsof the frame may be used as a mark for the synchronization data 2201,and the other bits may be used for another purpose, for example, forarbitrary data.

[0236] Further, while shown in this eighth embodiment is a systemoperating based on the transmission data frame of 48 kHz and based onthe transmission path frame of 44.1 kHz, they are not restricted tothese numeric values, and any system is applicable by changing thenumber of transmission data frames and the number of transmission pathframes as long as the system is one in which the clock sources of thetransmission data frame and the transmission path frame are common. Forexample, in a system operating based on the transmission data frame of44.1 kHz and based on the transmission path frame of 48 kHz, thesynchronization relationship that while 147 transmission data frames areinput, 160 transmission path frames are transmitted, is established, andtherefore in a case where when the data for 1 transmission path frameare of 64 bits, a transmission path for transmitting 64 bits in{fraction (1/48000)} second is reserved, data can be transmitted using147 transmission path frames and the remaining 13 transmission pathframes can be used for the transmission of synchronization data 2201 andarbitrary data.

EMBODIMENT 9

[0237] Next, a data transmission system and data transmission methodaccording to this ninth embodiment will be described. This ninthembodiment is characterized in that a method at the transmission to thetransmission path is different from that of the above-described eighthembodiment. Hereinafter, a description will be made with reference tothe drawings. Then, an apparatus configuration in this ninth embodimentis similar to that shown in FIG. 15, and the detailed description isomitted here.

[0238]FIG. 25 is a diagram illustrating a method of transmittingtransmission data frames in this ninth embodiment. Then, in this ninthembodiment, the relationship between the clock of the transmission dataand the clock of the transmission path frame is the same as that of theabove-described eighth embodiment. That is, 160 transmission data framesare transmitted with using 147 transmission path frames, therebyestablishing proper synchronization relationship.

[0239] In this ninth embodiment, as shown in FIG. 25(a), 1 bit of dummydata 2502 is added to the heads of the transmission path frames otherthan the transmission path frames including synchronization data 2501.The dummy data 2502 is for discriminating between the transmission pathframes and the transmission path frames including synchronization data2501 in the reception apparatus 1520.

[0240] Then, in this ninth embodiment, all the bits of thesynchronization data 2501 are set to “1” and the dummy data 2502 is setto “0”. By such definition, there arises no cases where all the bits ofthe transmission path frames other than the transmission path framesincluding the synchronization data 2501 are set to “1”, an erroneousdetection of the transmission path frames including the synchronizationdata 2501 is eliminated, thereby performing more reliable transmission.

[0241] To be specific, in this ninth embodiment, 64 bits of transmissiondata frame obtained by omitting nothing, which is shown in FIG. 25(c),are transmitted. Hence, the data amount for 160 frames are 160×64=10240bits. The number of frames required for transmitting these with usingthe transmission path frame is 10240/71=144.25 . . . since bits otherthan 1 bit of dummy data 2502 are used for transmission of thesignificant data 2503, and therefore 160 frames of transmission data canbe transmitted by using 145 transmission path frames.

[0242] The transmission data frames each of which is thus obtained bypacketizing as 64 bits all the transmission data (FIG. 25(c)) aresequentially combined (FIG. 25(b)), and thereafter are transmitted 71bits by 71 bits with using the transmission path frame (FIG. 25(a)). InFIG. 25, the transmission data frames 1, 2, . . . are transmitted in thetransmission path frames 3, 4, . . . respectively in this order, and thetransmission of a total of 10240 bits of up to the transmission pathframe 147, that is, 160 transmission frames, is completed. Then, thesignificant data 2503 of 10240−71×144=16 bits are transmitted in thelast transmission path frame 147, and the remaining 55 bits areinsignificant data 2504 (refer to FIG. 25(a) and FIG. 25(b)). Byrepeating these, the transmission data frames are continuouslytransmitted to the side of the reception apparatus 1520.

[0243] Then, the arbitrary data, for example, user data, the music datain the case of transmitting audio data as significant data, or the like,may be accommodated in the transmission path frame 2 and transmitted.

[0244] In this way, according to this ninth embodiment, in a systemoperating based on the transmission data clock of 48 kHz and thetransmission path clock of 44.1 kHz, the transmission apparatus 1510creates the transmission path clock from the transmission data clock inthe first clock control means 1501, sequentially combines thetransmission data frames and thereafter transmits the frames 71 bits by71 bits, which are added to 1 bit of dummy data, by using thetransmission path frame, and the reception apparatus 1520 receives thetransmission path frame and the transmission path clock, and creates thetransmission data clock from the transmission path clock in the secondclock control means 1527, and outputs the transmission data to the dataprocessing means 121 on the basis of the transmission data clock,thereby realizing the synchronized transmission between the transmissionapparatus 1510 and the reception apparatus 1520.

[0245] Then, also in this ninth embodiment, as in the above-describedeighth embodiment, any configuration may be adopted as long as theconfiguration is one in which the transmission data clock and thetransmission path clock are generated from the same clock source.

[0246] Further, a method of packet reception synchronization in thisninth embodiment is an example, and the method is not necessarilyrestricted thereto. For example, the transmission path frame 2 may beused for the arbitrary data transmission. Further, it is not necessarythat the whole transmission path frame 1 accommodate the synchronizationdata, and a portion of bits of the transmission path frame are used forthe transmission of the synchronization data, and the other bits may beused for another purpose, for example, for the transmission of arbitrarydata and the like.

[0247] Further, while in this ninth embodiment a system operating basedon the transmission data frame of 48 kHz and based on the transmissionpath frame of 44.1 kHz is shown, they are not restricted to thesenumeric values, and any system is applicable by changing the number oftransmission data frames and the number of transmission path frames aslong as the system is one in which the clock sources of the transmissiondata frame and the transmission path frame are common.

[0248] Further, a method of preventing an erroneous detection of thetransmission path frame including the synchronization data which is usedin this ninth embodiment, is also applicable to the above-describedsixth embodiment or seventh embodiment. For example, when theabove-described method of preventing an erroneous detection is appliedto the above-described seventh embodiment, 63 bits among 64 bits whichare reserved in each of the transmission path frames for transmittingthe significant data 2001 in FIG. 21 are used for transmitting thesignificant data 2001, and 1 bit is used as dummy data. At this time,since 8640÷63=137.14 . . . , 138 transmission path frames, that is,transmission path frame 10 to transmission path frame 147, are used forthe transmission of the significant data 2001. Only 8640−63×137=9 bitsare transmitted in the last transmission path frame 147, and theremaining 54 bits (=63−9) are insignificant data. Also in this case, thetransmission path frame 1 is used as a frame including synchronizationdata 2002, and the transmission path frame 2 to transmission path frame9 may be used for the transmission of user data in a like manner. Then,in this case, the first 1 bit of each of the transmission path frame 2to transmission path frame 9 is the dummy data and the remaining 63 bitsare used for the transmission of the user data.

[0249] Further, while in the above-described first to ninth embodimentscases where IEC60958 is used as a format of the transmission data andMOST is used as transmission path 100 are described, also when anothertransmission data format or another transmission path is used, they areapplicable in a like manner.

[0250] Further, the numeric values used in the above-described first toninth embodiments are examples, and the numeric values are notrestricted to these values in actual operation.

[0251] Further, the packet formats shown in the above-described first toseventh embodiments are examples, and the location of each field on thepacket and the like can be arbitrarily changed.

[0252] Further, the number of transmission path frames including thesynchronization data shown in FIG. 17, FIG. 21, FIG. 22, and FIG. 25 inthe above-described sixth to ninth embodiments or the location of thedummy data on the transmission path frame shown in FIG. 25 in theabove-described ninth embodiment is an example, and they can bearbitrarily changed.

[0253] Further, while in the above-described first to ninth embodimentsthe configurations in which the data generation means exist outside thetransmission apparatus are shown, the present invention can be similarlyrealized in a configuration in which the data generation means isincluded in the transmission apparatus.

[0254] Further, while in these first to ninth embodiments theconfigurations in which the data processing means exist outside thereception apparatus are shown, the present invention can be similarlyrealized in a configuration in which the data processing means isincluded in the reception apparatus.

[0255] Further, while in these first to seventh embodiments the preambleand parity portions are omitted in the transmission apparatus, a formatin which one of them, for example, a parity, is not omitted may betransmitted to the reception apparatus. Further, the configuration maybe one where when fields other than these, which are not used in thetransmission, are present, the transmission apparatus can omit thefields similarly to increase spare bits.

[0256] Further, while in these first to seventh embodiments, 1 frame oftransmission data is used as a processing unit, the present inventioncan be similarly realized also when a plurality of frames are used as aprocessing unit.

APPLICABILITY IN INDUSTRY

[0257] A data transmission system as well as data transmission method,data transmission apparatus and data reception apparatus according tothe present invention are useful as a system, method and apparatuseswhich can maintain synchronization between the transmission andreception even when the transmission apparatus, the reception apparatusand the transmission path do not operate on the same clock.

1. A data transmission system in which one or more transmissionapparatus and one or more reception apparatus are connected to eachother via a transmission path and data are transmitted from thetransmission apparatus to the reception apparatus with using an accessunit which emerges at certain time intervals and is allocated for thetransmission path, wherein the transmission apparatus comprises a datapacket generation means for receiving transmission data which iscomposed of consecutive data frames and has a format which includes apreamble indicating a start of the data frame, or a parity for detectingan error in the data frame, or both of them, and omitting the preamble,or the parity, or both of them, from one or more data frames included inthe transmission data received within the certain time intervals, addingto this resultant a data length field indicating the number of bits ofsignificant data, and setting the remaining spare portion as spare bits,thereby generating a data packet composing the access unit over itsentire length, and the reception apparatus comprises a data extractionmeans for receiving the access unit, and adding the preamble, or theparity, or both of them, which have been omitted by the data packetgeneration means, thereby reconstructing the data frame:
 2. The datatransmission system as defined in claim 1, wherein the receptionapparatus comprises: a buffer means for temporarily accumulating thedata frames reconstructed by the data extraction means, and a buffercontrol means for monitoring the accumulated data amount in the buffermeans and adjusting a data reading rate from the buffer means inaccordance with the increase or decrease in the accumulated data amount.3. The data transmission system as defined in claim 1, wherein thetransmission apparatus comprises a time-information generation means forgenerating a time based on a clock of the transmission data, wherein thedata packet generation means also adds the time-information as well asthe data length field and sets the remaining spare portion as sparebits, thereby composing the access unit over the entire length, and thereception apparatus comprises: a buffer means for temporarilyaccumulating the data frames reconstructed by the data extraction means,a clock control means for reproducing the time generated by thetransmission apparatus by using the time-information which the dataextraction means read from within the access unit constructed by thedata packet generation means, and a buffer control means for adjusting adata reading rate from the buffer means based on a clock which issynchronized with a time reproduced by the clock control means.
 4. Thedata transmission system as defined in claim 1, wherein, the data packetgeneration means also adds a preamble location pointer indicating alocation of the first preamble in the data frame, and a type of thepreamble of the data frame, the preamble being indicated by the preamblelocation pointer, as well as the data length field, and setting theremaining spare portion as spare bits, thereby constructing the accessunit over the entire length.
 5. The data transmission system as definedin claim 1, wherein, the transmission data format includes a specificfield having a value specific to an application, the data packetgeneration means also omits the specific field as well as the preamble,or the parity, or both of them, and the data extraction means also addsthe specific field as well as the preamble, or the parity, or both ofthem, thereby reconstructing the data frame.
 6. The data transmissionsystem as defined in claim 1, wherein the data length field indicatesthe number of bits of spare bits.
 7. A data transmission system in whichone or more transmission apparatus and one or more reception apparatusare connected to each other via a transmission path and data aretransmitted from the transmission apparatus to the reception apparatuswith using an access unit which emerges at certain time intervals and isallocated for the transmission path, wherein the transmission apparatuscomprises a data packet generation means for receiving transmission datawhich is composed of consecutive data frames and has a data transferrate, a relationship of an integer ratio being established between thedata transfer rate and a data transfer rate allocated for thetransmission path, grouping into a processing unit a plurality of thedata frames of the received transmission data and corresponding to aperiod equal to an integral multiple of the time intervals at which theaccess unit emerges, dividing the processing unit into transmission pathframes each of which is the data amount which can be accommodated in theaccess unit, thereby generating a data packet composing the access unitincluding the transmission path frame, and the reception apparatuscomprises a data extraction means for receiving the access unit,reconstructing the processing unit from one or more of the receivedaccess units, and further reconstructing the consecutive data frames. 8.The data transmission system as defined in claim 7, wherein the datapacket generation means enters one or more bits of synchronization dataindicating a start of the processing unit into one or more access units,and the data extraction means detects the starting location of theprocessing unit by receiving the synchronization data.
 9. The datatransmission system as defined in claim 8, wherein the data packetgeneration means enters one or more bits of discrimination data whichare different from a value of the synchronization data, whichdiscrimination data indicate that the synchronization data are notincluded in the access unit, into position in the access unit in whichthe synchronization data are not entered.
 10. A data transmission systemin which one or more transmission apparatus and one or more receptionapparatus are connected to each other via a transmission path and dataare transmitted from the transmission apparatus to the receptionapparatus with using an access unit which emerges at certain timeintervals and is allocated for the transmission path, wherein thetransmission apparatus comprises a data packet generation means forreceiving transmission data which is composed of consecutive dataframes, has a data transfer rate, a relationship of an integer ratiobeing established between the data transfer rate and a data transferrate allocated for the transmission path, and has a format including apreamble indicating a start of the data frame, or a parity for detectingan error in the data frame, or both of them, omitting the preambles, orthe parities, or both of them, from a plurality of the data frames ofthe received transmission data and corresponding to a period equal to anintegral multiple of the time intervals at which the access unit emergesto set the resultant as one processing unit, dividing the processingunit into transmission path frames each of which is the data amountwhich can be accommodated in the access unit, thereby generating a datapacket composing the access unit including the transmission path frame,and the reception apparatus comprises a data extraction means forreceiving the access unit, reconstructing the processing unit from oneor more of the received access units, and further adding the preambles,or the parities, or both of them, which have been omitted by the datapacket generation means, thereby reconstructing the data frames.
 11. Thedata transmission system as defined in claim 10, wherein the data packetgeneration means enters one or more bits of synchronization dataindicating a start of the processing unit into one or more access units,and the data extraction means detects the starting location of theprocessing unit by receiving the synchronization data.
 12. The datatransmission system as defined in claim 11, wherein the data packetgeneration means enters one or more bits of discrimination data whichare different from a value of the synchronization data, whichdiscrimination data indicate that the synchronization data are notincluded in the access unit, into position in the access unit in whichthe synchronization data are not entered.
 13. The data transmissionsystem as defined in claim 10, wherein the transmission data formatincludes a specific field having a value specific to an application, andthe data packet generation means also omits the specific field as wellas the preamble, or the parity, or both of them, and the data extractionmeans also adds the specific field as well as the preamble, or theparity, or both of them, thereby reconstructing the data frame.
 14. Thedata transmission system as defined in any claim 1, wherein thetransmission data format is a format defined by IEC60958.
 15. The datatransmission system as defined in claim 1, wherein the transmission pathis a serial bus.
 16. A data transmission apparatus connected to atransmission path, which transmits data with using an access unitallocated for the transmission path, the data transmission apparatuscomprising a data packet generation means for receiving transmissiondata which is composed of consecutive data frames and has a format whichincludes a preamble indicating a start of the data frame, or a parityfor detecting an error in the data frame, or both of them, omitting thepreamble or the parity, or both of them, from one or more data framesincluded in the transmission data transmitted with using the accessunit, adding to this resultant a data length field indicating the numberof bits of significant data, and setting the remaining spare portion asspare bits, thereby generating a data packet composing the access unitover its entire length.
 17. The data transmission apparatus as definedin claim 16, comprising a time-information generation means forgenerating a time based on a clock of the transmission data, wherein thedata packet generation means also adds the time-information as well asthe data length field, and sets the remaining spare portion as sparebits, thereby generating a data packet composing an access unit over itsentire length.
 18. The data transmission apparatus as defined in claim16, wherein the data packet generation means also adds a preamblelocation pointer indicating a location of the first preamble in the dataframe, and a type of the preamble of the data frame, the preamble beingindicated by the preamble location pointer, as well as the data lengthfield, and sets the remaining spare portion as spare bits, therebygenerating a data packet composing the access unit over its entirelength.
 19. The data transmission apparatus as defined in any of claim16, wherein the transmission data format includes a specific fieldhaving a value specific to an application, and the data packetgeneration means also omits the specific field as well as the preamble,or the parity, or both of them.
 20. The data transmission apparatus asdefined in claim 16, wherein the data length field indicates the numberof bits of spare bits.
 21. A data transmission apparatus connected to atransmission path, which transmits data with using an access unit whichemerges at certain time intervals and is allocated for the transmissionpath, the data transmission apparatus comprising a data packetgeneration means for receiving transmission data which is composed ofconsecutive data frames and has a data transfer rate, a relationship ofan integer ratio being established between the data transfer rate and adata transfer rate allocated for the transmission path, grouping into aprocessing unit a plurality of the data frames of the receivedtransmission data and corresponding to a period equal to an integralmultiple of the time intervals at which the access unit emerges,dividing the processing unit into transmission path frames each of whichis the data amount which can be accommodated in the access unit, therebygenerating a data packet composing the access unit including thetransmission path frame.
 22. The data transmission apparatus as definedin claim 21, wherein the data packet generation means enters one or morebits of synchronization data indicating a start of the processing unitinto one or more access units.
 23. The data transmission apparatus asdefined in claim 22, wherein the data packet generation means enters oneor more bits of discrimination data which are different from a value ofthe synchronization data, which discrimination data indicate that thesynchronization data are not included in the access unit, into positionin the access unit in which the synchronization data are not entered.24. A data transmission apparatus connected to a transmission path,which transmits data with using an access unit which emerges at certaintime intervals and is allocated for the transmission path, the datatransmission apparatus comprising a data packet generation means forreceiving transmission data which is composed of consecutive dataframes, has a data transfer rate, a relationship of an integer ratiobeing established between the data transfer rate and a data transferrate allocated for the transmission path, and has a format including apreamble indicating a start of the data frame, or a parity for detectingan error in the data frame, or both of them, omitting the preambles, orthe parities, or both of them, from a plurality of the data frames ofthe received transmission data and corresponding to a period equal to anintegral multiple of the time intervals at which the access unit emergesto set the resultant as one processing unit, dividing the processingunit into transmission path frames each of which is the data amountwhich can be accommodated in the access unit, thereby generating a datapacket composing the access unit including the transmission path frame.25. The data transmission apparatus as defined in claim 24, wherein thedata packet generation means enters one or more bits of synchronizationdata indicating a start of the processing unit into one or more accessunits.
 26. The data transmission apparatus as defined in claim 25,wherein the data packet generation means enters one or more bits ofdiscrimination data which are different from a value of thesynchronization data, which discrimination data indicate that thesynchronization data are not included in the access unit, into positionin the access unit in which the synchronization data are not entered.27. The data transmission apparatus as defined in claim 24, wherein thetransmission data format includes a specific field having a valuespecific to an application, and the data packet generation means alsoomits the specific field as well as the preamble, or the parity, or bothof them.
 28. The data transmission apparatus as defined in claim 16,wherein the transmission data format is a format defined by IEC60958.29. The data transmission apparatus as defined in claim 16, wherein thetransmission path is a serial bus.
 30. A data reception apparatus whichis connected to a transmission path and receives a data packet obtainedby omitting the preamble, or the parity, or both of them, from one ormore data frames included in the transmission data which are transmittedwith using an access unit which emerges at certain time intervals and isallocated for the transmission path, adding to this resultant a datalength field indicating the number of bits of significant data, settingthe remaining spare portion as spare bits and composing the access unitover its entire length, the data reception apparatus comprising a dataextraction means for receiving the access unit and adding thereto thepreamble of the transmission data, or the parity thereof, or both ofthem, which have been omitted, thereby reconstructing the data frame.31. The data reception apparatus as defined in claim 30, comprising: abuffer means for temporarily accumulating the reconstructed data frames,and a buffer control means for monitoring the accumulated data amount inthe buffer means and adjusting a data reading rate from the buffer meansin accordance with the increase or decrease in the accumulated dataamount.
 32. The data reception apparatus as defined in claim 30,comprising: a buffer means for temporarily accumulating thereconstructed data frames, a clock control means for reproducing a timewith using time-information which the data extraction means read fromwithin the constructed access unit, and a buffer control means foradjusting a data reading rate from the buffer means based on a clockwhich is synchronized with a time reproduced by the clock control means.33. A data reception apparatus which is connected to a transmission pathand which receives a data packet obtained by omitting preambles eachindicating a start of a data frame, or parities for detecting errors inthe data frames, or both of them, from a plurality of data framescorresponding to a period equal to an integral multiple of timeintervals at which the access unit emerges, which data frames aretransmitted with using the access unit which emerges at certain timeintervals and is allocated for the transmission path, to set theresultant as one processing unit, and dividing the processing unit intotransmission path frames each of which is the data amount which can beaccommodated in the access unit, and composing the access unit includingthe transmission path frame, the data reception apparatus comprising adata extraction means for receiving the access unit, reconstructing theprocessing unit from one or more of the received access units, adding tothe processing unit the omitted preamble or parity, or both of them,thereby reconstructing the data frame.
 34. The data reception apparatusas defined in claim 33, wherein the data extraction means detects thestarting location of the processing unit by receiving one or more accessunits including one or more bits of synchronization data indicating thestart of the processing unit.
 35. The data reception apparatus asdefined in claim 30, wherein the transmission data format includes aspecific field having a value specific to an application, and the dataextraction means adds the specific field as well as the preamble, or theparity, or both of them, according to a data frame of the transmissiondata, thereby reconstructing the data frame.
 36. The data receptionapparatus as defined in claim 30, wherein the transmission data formatis a format defined by IEC60958.
 37. The data reception apparatus asdefined in claim 30, wherein the transmission path is a serial bus. 38.A data transmission method comprising: a data packet generation step ofomitting a preamble indicating a start of a data frame, or a parity fordetecting an error in the data frame, or both of them, from one or moredata frames included in the transmission data which is composed ofconsecutive data frames and has a format which includes the preamble, orthe parity, or both of them, adding to this resultant a data lengthfield indicating the number of bits of significant data of the frame,and setting the remaining spare portion as spare bits, and composing anaccess unit allocated for the transmission path over the entire length,thereby transmitting the access unit to the transmission path, and adata extraction step of receiving the access unit and adding to theaccess unit the preamble or the parity, or both of them, which have beenomitted in the data packet generation step, thereby reconstructing thedata frame.
 39. The data transmission method as defined in claim 38,wherein the transmission data format includes a specific field having avalue specific to an application, the data packet generation step omitsthe specific field as well as the preamble, or the parity, or both ofthem, and the data extraction step also adds the specific field as wellas the preamble, or the parity, or both of them, thereby reconstructinga frame.
 40. A data transmission method comprising: a data packetgeneration step of receiving transmission data which has a data transferrate, a relationship of an integer ratio being established between thedata transfer rate and a data transfer rate allocated for a transmissionpath, and which transmission data is composed of consecutive dataframes, grouping into a processing unit a plurality of the data framesof the received transmission data and corresponding to a period equal toan integral multiple of time intervals at which the access unit emerges,dividing the processing unit into transmission path frames each of whichis the data amount which can be accommodated in the access unit, therebygenerating a data packet composing the access unit including thetransmission path frame, and a data extraction step of receiving theaccess unit, reconstructing the processing unit from one or more of thereceived access units, and further reconstructing the consecutive dataframes.
 41. A data transmission method comprising: a data packetgeneration step of receiving transmission data which has a data transferrate, a relationship of an integer ratio being established between thedata transfer rate and a data transfer rate allocated for a transmissionpath, and which transmission data is composed of consecutive data framesand has a format including a preamble indicating a start of the dataframe, or a parity for detecting an error in the data frame, or both ofthem, omitting the preamble, or the parity, or both of them, from aplurality of the data frames of the received transmission data andcorresponding to a period equal to an integral multiple of timeintervals at which the access unit emerges to set the resultant as oneprocessing unit, dividing the processing unit into transmission pathframes each of which is the data amount which can be accommodated in theaccess unit, thereby generating a data packet composing the access unitincluding the transmission path frame, and a data extraction step ofreceiving the access unit, reconstructing the processing unit from oneor more of the received access units, adding to the processing unit thepreamble, or the parity, or both of them, which have been omitted in thedata packet generation step, thereby reconstructing the data frame. 42.The data transmission method as defined in claim 41, wherein thetransmission data format includes a specific field having a valuespecific to an application, the data packet generation step omits thespecific field as well as the preamble, or the parity, or both of them,and the data extraction step also adds the specific field as well as thepreamble, or the parity, or both of them, thereby reconstructing aframe.
 43. The data transmission system as defined in claim 10, whereinthe transmission data format is a format defined by IEC60958.
 44. Thedata transmission system as defined in claim 7, wherein the transmissionpath is a serial bus.
 45. The data transmission system as defined inclaim 10, wherein the transmission path is a serial bus.
 46. The datatransmission apparatus as defined in claim 24, wherein the transmissiondata format is a format defined by IEC60958.
 47. The data transmissionapparatus as defined in claim 21, wherein the transmission path is aserial bus.
 48. The data transmission apparatus as defined in claim 24,wherein the transmission path is a serial bus.
 49. The data receptionapparatus as defined in claim 33, wherein the transmission data formatincludes a specific field having a value specific to an application, andthe data extraction means adds the specific field as well as thepreamble, or the parity, or both of them, according to a data frame ofthe transmission data, thereby reconstructing the data frame.
 50. Thedata reception apparatus as defined in claim 33, wherein thetransmission data format is a format defined by IEC60958.
 51. The datareception apparatus as defined in claim 33, wherein the transmissionpath is a serial bus.